Bipolar II disorder (BP-II; pronounced "type two bipolar" or "bipolar type two" disorder) is a bipolar spectrum disorder (see also: Bipolar I disorder) characterized by at least one episode of hypomania and at least one episode of major depression.[1][2][3][4] Diagnosis for bipolar II disorder requires that the individual must never have experienced a full manic episode (unless caused by an antidepressant;[5] otherwise one manic episode meets the criteria for bipolar I disorder).[2]
Hypomania is a sustained state of elevated or irritable mood that is less severe than mania and does not significantly impact quality of life. Unlike mania, hypomania is not  associated with psychosis.[1] The hypomanic episodes associated with bipolar II disorder must last for at least four days.[2][6] Commonly, depressive episodes are more frequent and more intense than hypomanic episodes.[2][7] Additionally, when compared to bipolar I disorder, type II presents more frequent depressive episodes and shorter intervals of well-being.[1][2] The course of bipolar II disorder is more chronic and consists of more frequent cycling than the course of bipolar I disorder.[1][8] Finally, bipolar II is associated with a greater risk of suicidal thoughts and behaviors than bipolar I or unipolar depression.[1][8] Although bipolar II is commonly perceived to be a milder form of Type I, this is not the case.  Types I and II present equally severe burdens.[1][9]
Bipolar II is notoriously difficult to diagnose. Patients usually seek help when they are in a depressed state, or when their hypomanic symptoms manifest themselves in unwanted effects, such as high levels of anxiety, or the seeming inability to focus on tasks. Because many of the symptoms of hypomania are often mistaken for high functioning behavior or simply attributed to personality, patients are typically not aware of their hypomanic symptoms. In addition, many people who suffer from Bipolar II have periods of normal affect. As a result, when patients seek help, they are very often unable to provide their doctor with all the information needed for an accurate assessment; these individuals are often misdiagnosed with unipolar depression.[1][2][8] Of all individuals initially diagnosed with major depressive disorder, between 40% and 50% will later be diagnosed with either BP-I or BP-II.[1] Substance abuse disorders (which have high co-morbidity with BP-II) and periods of mixed depression may also make it more difficult to accurately identify BP-II.[2] Despite the difficulties, it is important that BP-II individuals be correctly assessed so that they can receive the proper treatment.[2] Antidepressant use, in the absence of mood stabilizers, is correlated with worsening BP-II symptoms.[1]
Signs and symptoms
Hypomanic episodes
Hypomania is the signature characteristic of Bipolar II disorder. It is a state characterized by euphoria and/or an irritable mood.  In order for an episode to qualify as hypomanic, the individual must also present three or more of the below symptoms, and last at least four consecutive days and be present most of the day, nearly every day[1][2]
Inflated self-esteem or grandiosity.
Decreased need for sleep (e.g., feels rested after only 3 hours of sleep).
More talkative than usual or pressure to keep talking.
Flight of ideas or subjective experience that thoughts are racing.
Distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli), as reported or observed.
Increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation.
Excessive involvement in activities that have a high potential for painful consequences (e.g., engaging in unrestrained buying sprees, sexual indiscretions, or foolish business investments).
It is important to distinguish between hypomania and mania. Mania is generally greater in severity and impairs function, sometimes leading to hospitalization and in the most severe cases, psychosis.  In contrast, hypomania usually increases functioning.  For this reason, it is not uncommon for hypomania to go unnoticed. Often it is not until individuals are in a depressive episode that they seek treatment, and even then their history of hypomania may go undiagnosed. Even though hypomania may increase functioning, episodes need to be treated because they may precipitate a depressive episode.[1][2]
Depressive episodes
It is during depressive episodes that BP-II patients often seek help.  Symptoms may be syndromal or subsyndromal.[1] Depressive BP-II symptoms may include five or more of the below symptoms (at least one of them must be either depressed mood or loss of interest/pleasure). In order to be diagnosed, they need to be present only during the same two-week period, as a change from previous hypomanic functioning:
Depressed mood most of the day, nearly every day, as indicated by either subjective report (e.g., feels sad, empty, or hopeless) or observation made by others (e.g., appears tearful). (Note: In children and adolescents, can be irritable mood.)
Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day (as indicated by either subjective account or observation).
Significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day. (Note: In children, consider failure to make expected weight gain.)
Insomnia or hypersomnia nearly every day.
Psychomotor agitation or retardation nearly every day (observable by others; not merely subjective feelings of restlessness or being slowed down).
Fatigue or loss of energy nearly every day.
Feelings of worthlessness or excessive or inappropriate guilt nearly every day (not merely self-reproach or guilt about being sick).
Diminished ability to think or concentrate, possible irritability or indecisiveness, nearly every day (either by subjective account or as observed by others).
Recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, a suicide attempt, or a specific plan for committing suicide.
Evidence also suggests that BP-II is strongly associated with atypical depression. Essentially, this means that many BP-II patients exhibit reverse vegetative symptoms. BP-II patients may have a tendency to oversleep and overeat, while typically depressed patients sleep and eat less than usual.[1][8]
Mixed depression
Depressive mixed states occur when patients experience depression and non-euphoric, usually subsyndromal, hypomania at the same time. As mentioned previously, it is particularly difficult to diagnose BP-II when a patient is in this state.
In a mixed state, mood is depressed, but the following symptoms of hypomania present as well:
Irritability
Mental overactivity
Behavioral overactivity
Mixed states are associated with greater levels of suicidality than non-mixed depression. Antidepressants may increase this risk.[1][2]
Relapse
In the case of a relapse, the following symptoms often occur and are considered early warning signs:[10]
Sleep disturbance: patient requires less sleep and does not feel tired
Racing thoughts and/or speech
Anxiety
Irritability
Emotional intensity
Spending more money than usual
Binge behavior, including food, drugs, or alcohol
Arguments with family members and friends
Taking on many projects at once
People with bipolar disorder may develop dissociation to match each mood they experience. For some, this is done intentionally,  as a means by which to escape trauma or pain from a depressive period, or simply to better organize one's life by setting boundaries for one's perceptions and behaviors.[11]
Studies indicate that the following events may also precipitate relapse in BP-II patients:[12]
Stressful life events
Relatives' or peers' criticism
Antidepressant use
Disrupted circadian rhythm
Causes
Scientists are studying the possible causes of bipolar disorder and most agree that there is no single cause.[13] There have been very few studies conducted to examine the possible causes of Bipolar II. Those that have been done have not considered Bipolar I and Bipolar II separately and have had inconclusive results. Researchers have found that patients with either Bipolar I or II may have increased levels of blood calcium concentrations, but the results are inconclusive. The studies that have been conducted did not find a significant difference between those with Bipolar I or Bipolar II. There has been a study looking at genetics of Bipolar II disorder and the results are inconclusive; however, scientists did find that relatives of people with Bipolar II are more likely to develop the same bipolar disorder or major depression rather than developing Bipolar I disorder.[10]
Diagnosis
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) recognizes two types of bipolar disorders—bipolar I and bipolar II. People with bipolar I disorder suffer from at least one manic or mixed episode, and may experience depressive episodes. On the contrary, as noted above, people with bipolar II disorder experience a milder form of a manic episode, known as a hypomanic episode as well as major depressive episodes. Although bipolar II is thought to be less severe than bipolar I in regards to symptom intensity, it is actually more severe and distressing with respect to episode frequency and overall course. Those with bipolar II often experience more frequent bouts of depressive episodes.[14] Specific criteria defined by the DSM-IV for a bipolar II diagnosis is as follows:
The presence of a hypomanic or major depressive episode.
If currently in major depressive episode, history of a hypomanic episode. If currently in a hypomanic episode, history of a major depressive episode. No history of a manic episode.
Significant stress or impairment in social, occupational, or other important areas of functioning.[5]
Studies have identified major differences between bipolar I and bipolar II in regards to their clinical features, comorbidity rates and family histories. According to Baek et al. (2011), during depressive episodes, bipolar II patients tend to show higher rates of psychomotor agitation, guilt, shame, suicidal ideation, and suicide attempts. Bipolar II patients have shown higher lifetime comorbidity rates of DSM axis I diagnoses such as phobias, anxiety disorders, substance & alcohol abuse, and eating disorders and there is a higher correlation between bipolar II patients and family history of psychiatric illness, including major depression and substance-related disorders. The occurrence rate of psychiatric illness in first degree relatives of bipolar II patients was 26.5%, versus 15.4% in bipolar I patients.[14][15]
Screening instruments like the Mood Disorders Questionnaire (MDQ) are helpful tools in determining a patient's status on the bipolar spectrum and getting families involved can also improve chances of an accurate diagnosis and acknowledgment of hypomanic episodes. In addition, there are certain features that have been shown to increase the chances that depressed patients are suffering from a bipolar disorder including atypical symptoms of depression like hypersomnia and hyperphagia, a family history of bipolar disorder, medication-induced hypomania, recurrent or psychotic depression, antidepressant refractory depression, and early or postpartum depression.[15]
Treatments
Treatment typically includes three things: the treatment of acute hypomania, the treatment of acute depression, and the prevention of the relapse of either hypomania or depression.  The main goal is to make sure that patients do not harm themselves.[16]
Pharmaceutical therapies
The most common treatment for reducing bipolar II disorder symptoms is medication, usually in the form of mood stabilizers. However, treatment with mood stabilizers may produce a flat affect in the patient, which is dose-dependent. Concurrent use of SSRI antidepressants may help some with bipolar II disorder, though these medications should be used with caution because it is believed that they may cause a hypomanic switch.[16]
The pharmaceutical management of bipolar II disorder is not generally supported by strong evidence, with limited randomised controlled trials (RCTs) published in the literature. Some medications used are:[16]
Lithium - There is strong evidence that lithium is effective in treating both the depressive and hypomanic symptoms in bipolar II. In addition, its action as a mood stabilizer can be used to decrease the risk of hypomanic switch in patients treated with antidepressants.
Anticonvulsants - there is evidence that lamotrigine decreases the risk of relapse in rapid cycling bipolar II. It appears to be more effective in bipolar II than bipolar I, suggesting that lamotrigine is more effective for the treatment of depressive rather than manic episodes. Doses ranging from 100–200mg have been reported to have the most efficacy, while experimental doses of 400mg have rendered little response.[17] A large, multicentre trial comparing carbamazepine and lithium over two and a half years found that carbamazepine was superior in terms of preventing future episodes of bipolar II, although lithium was superior in individuals with bipolar I. There is also some evidence for the use of valproate and topiramate, although the results for the use of gabapentin have been disappointing.
Antidepressants - there is evidence to support the use of SSRI and SNRI antidepressants in bipolar II. Indeed, some sources consider them to be one of the first line treatments.[18]  However, antidepressants also pose significant risks, including a switch to mania, rapid cycling, and dysphoria[19] and so many psychiatrists advise against their use for bipolar. When used, antidepressants are typically combined with a mood stabilizer.
Antipsychotics - there is good evidence for the use of quetiapine, and it has been approved by the FDA for this indication. There is also some evidence for the use of risperidone, although the relevant trial was not placebo controlled and was complicated by the use of other medications in some of the patients.
Dopamine agonists - there is evidence for the efficacy of pramipexole from one randomized control trial.
Non-pharmaceutical therapies
Non-pharmaceutical therapies can also help those with the illness. These include cognitive behavioral therapy (CBT), psychodynamic therapy, psychoanalysis, social rhythm therapy,  interpersonal therapy, behavioral therapy, cognitive therapy, art therapy, music therapy, psychoeducation, mindfulness, light therapy, and family-focused therapy. Relapse can still occur, even with continued medication and therapy.[20]
Prognosis
There is evidence to suggest that bipolar II has a more chronic course of illness than bipolar I disorder.[21] This constant and pervasive course of the illness leads to an increased risk in suicide and more hypomanic and major depressive episodes with shorter periods between episodes than bipolar I patients experience.[21] The natural course of bipolar II disorder, when left untreated, leads to patients spending the majority of their lives unwell with much of their suffering stemming from depression.[15] Their recurrent depression results in personal suffering and disability.[15]
This disability can present itself in the form of psychosocial impairment, which has been suggested to be worse in bipolar II patients than in bipolar I patients.[22] Another facet of this illness that is associated with a poorer prognosis is rapid cycling, which denotes the occurrence of four or more major Depressive, Hypomanic, and/or mixed episodes in a 12-month period.[21] Rapid cycling is quite common in those with Bipolar II, much more so in women than in men (70% vs. 40%), and without treatment leads to added sources of disability and an increased risk of suicide.[15] To improve a patient’s prognosis, long-term therapy is most favorably recommended for controlling symptoms, maintaining remission and preventing relapses.[23] With treatment, patients have been shown to present a decreased risk of suicide (especially when treated with lithium) and a reduction of frequency and severity of their episodes, which in turn moves them toward a stable life and reduces the time they spend ill.[24] To maintain their state of balance, therapy is often continued indefinitely, as around 50% of the patients who discontinue it relapse quickly and experience either full-blown episodes or sub-syndromal symptoms that bring significant functional impairments.[23]
Functioning
The deficits in functioning associated with Bipolar II disorder stem mostly from the recurrent depression that Bipolar II patients suffer from. Depressive symptoms are much more disabling than hypomanic symptoms and are potentially as, or more disabling than mania symptoms.[22] Functional impairment has been shown to be directly linked with increasing percentages of depressive symptoms, and because sub-syndromal symptoms are more common—and frequent—in Bipolar II disorder, they have been implicated heavily as a major cause of psychosocial disability.[15] There is evidence that shows the mild depressive symptoms, or even sub-syndromal symptoms, are responsible for the non-recovery of social functioning, which furthers the idea that residual depressive symptoms are detrimental for functional recovery in patients being treated for Bipolar II.[25] It has been suggested that symptom interference in relation to social and interpersonal relationships in Bipolar II Disorder is worse than symptom interference in other chronic medical illnesses such as cancer.[25] This social impairment can last for years, even after treatment that has resulted in a resolution of mood symptoms.[25]
The factors related to this persistent social impairment are residual depressive symptoms, limited illness insight (a very common occurrence in patients with Bipolar II Disorder), and impaired executive functioning.[25] Impaired ability in regards to executive functions is directly tied to poor psychosocial functioning, a common side-effect in patients with Bipolar II.[26]
The impact on a patient's psychosocial functioning stems from the depressive symptoms (more common in Bipolar II than Bipolar I).[22] An increase in these symptoms' severity seems to correlate with a significant increase in psychosocial disability.[26] Psychosocial disability can present itself in poor semantic memory, which in turn affects other cognitive domains like verbal memory and (as mentioned earlier) executive functioning leading to a direct and persisting impact on psychosocial functioning.[27]
An abnormal semantic memory organization can manipulate thoughts and lead to the formation of delusions and possibly affect speech and communication problems, which can lead to interpersonal issues.[27] Bipolar II patients have also been shown to present worse cognitive functioning than those patients with Bipolar I, though they demonstrate about the same disability when it comes to occupational functioning, interpersonal relationships, and autonomy.[26] This disruption in cognitive functioning takes a toll on their ability to function in the workplace, which leads to high rates of work loss in Bipolar II patient populations.[22] After treatment and while in remission, Bipolar II patients tend to report a good psychosocial functioning but they still score less in that department than patients without the disorder.[15] These lasting impacts further suggest that a prolonged exposure to an untreated Bipolar II disorder can lead to permanent adverse effects on functioning.[25]
Recovery and recurrence
Bipolar II Disorder has a chronic relapsing nature.[23] It has even been suggested that Bipolar II patients have a higher degree of relapse than Bipolar I patients.[21] Generally, within four years of an episode, around 60% of patients will relapse into another episode.[23] Some patients are even symptomatic half the time, either with full on episodes or symptoms that fall just below the threshold of an episode.[23]
Because of the nature of the illness, long-term therapy is the best option and aims to not only control the symptoms but to maintain sustained remission and prevent relapses from occurring.[23] Even with treatment, patients do not always regain full functioning, especially in the social realm.[25] There is a very clear gap between symptomatic recovery and full functional recovery for both Bipolar I and Bipolar II patients.[26] As such, and because those with Bipolar II spend more time with depressive symptoms that do not quite qualify as a major depressive episode, the best chance for recovery is to have therapeutic interventions that focus on the residual depressive symptoms and to aim for improvement in psychosocial and cognitive functioning.[26] Even with treatment, a certain amount of responsibility is placed in the patient's hands; they have to be able to assume responsibility for their illness by accepting their diagnosis, taking the required medication, and seeking help when needed to do well in the future.[28]
Treatment often lasts after remission is achieved, and the treatment that worked is continued during the continuation phase (lasting anywhere from 6–12 months) and maintenance can last 1–2 years or, in some cases, indefinitely.[29] One of the treatments of choice is Lithium, which has been shown to be very beneficial in reducing the frequency and severity of depressive episodes.[24] Lithium prevents mood relapse and works especially well in Bipolar II patients who experience rapid-cycling.[24] Almost all Bipolar II patients who take lithium have a decrease in the amount of time they spend ill and a decrease in mood episodes.[24]
Along with medication, other forms of therapy have been shown to be beneficial for Bipolar II patients. A treatment called a "well-being plan" serves several purposes: it informs the patients, protects them from future episodes, teaches them to add value to their life, and works toward building a strong sense of self to fend off depression and reduce the desire to succumb to the seductive hypomanic highs.[28] The plan has to aim high. Otherwise, patients will relapse into depression.[28] A large part of this plan involves the patient being very aware of warning signs and stress triggers so that they take an active role in their recovery and prevention of relapse.[28]
Mortality
Several studies have shown that the risk of suicide is higher in patients who suffer from Bipolar II than those who suffer from Bipolar I, and especially higher than patients who suffer from major depressive disorder.[15]
In results of a summary of several lifetime study experiments, it was found that 24% of Bipolar II patients experienced suicidal ideation or suicide attempts compared to 17% in Bipolar I patients and 12% in major depressive patients.[15][30] Bipolar disorders, in general, are the third leading cause of death in 15- to 24-year-olds.[31] Bipolar II patients were also found to employ more lethal means and have more complete suicides overall.[15]
Bipolar II patients have several risk factors that increase their risk of suicide. The illness is very recurrent and results in severe disabilities, interpersonal relationship problems, barriers to academic, financial, and vocational goals, and a loss of social standing in their community, all of which increase the likelihood of suicide.[32] Mixed symptoms and rapid-cycling, both very common in Bipolar II, are also associated with an increased risk of suicide.[15] The tendency for Bipolar II to be misdiagnosed and treated ineffectively, or not at all in some cases, leads to an increased risk.[30]
As a result of the high suicide risk for this group, reducing the risk and preventing attempts remains a main part of the treatment; a combination of self-monitoring, close supervision by a therapist, and faithful adherence to their medication regimen will help to reduce the risk and prevent the likelihood of a completed suicide.[32]
Suicide, which is both a stereotypic yet highly individualized act, is a common endpoint for many patients with severe psychiatric illness. The mood disorders (depression and bipolar manic-depression) are by far the most common psychiatric conditions associated with suicide. At least 25% to 50% of patients with bipolar disorder also attempt suicide at least once. With the exception of lithium--which is the most demonstrably effective treatment against suicide-remarkably little is known about specific contributions of mood-altering treatments to minimizing mortality rates in persons with major mood disorders in general and bipolar depression in particular. Suicide is usually a manifestation of severe psychiatric distress that is often associated with a diagnosable and treatable form of depression or other mental illness. In a clinical setting, an assessment of suicidal risk must precede any attempt to treat psychiatric illness.[33]
Comorbid conditions
Comorbid conditions are extremely common in individuals with BP-II. In fact, individuals are twice as likely to present a comorbid disorder than not.[2] These include anxiety, eating, personality (cluster B), and substance use disorders.[2][8] For bipolar II disorder, the most conservative estimate of lifetime prevalence of alcohol or other drug abuse disorders is 20%. In patients with comorbid substance abuse disorder and BP-II, episodes have a longer duration and treatment compliance decreases. Preliminary studies suggest that comorbid substance abuse is also linked to increased risk of suicidality.[34] The question of which condition should be designated the index and which the comorbid condition is not self-evident and may vary in relation to the research question, the disease that prompted a particular episode of care, or of the specialty of the attending physician. A related notion is that of complication, a condition that coexists or ensues, as defined in the Medical Subject Headings (MeSH)-controlled vocabulary maintained by the National Library of Medicine (NLM).[35]
History and future directions
In 19th century psychiatry, mania had a broad meaning of craziness, and hypomania was equated by some to concepts of 'partial insanity' or monomania. A more specific usage was advanced by the German neuro-psychiatrist Emanuel Ernst Mendel in 1881, who wrote "I recommend (taking under consideration the word used by Hippocrates) to name those types of mania that show a less severe phenomenological picture, 'hypomania'".[36] Narrower operational definitions of hypomania were developed from the 1960s/1970s.
The first diagnostic distinction to be made between manic-depression involving mania, and that involving hypomania, came from Carl Gustav Jung in 1903.[37][38] In his paper, Jung introduced the non-psychotic version of the illness with the introductory statement, "I would like to publish a number of cases whose peculiarity consists in chronic hypomanic behaviour" where "it is not a question of real mania at all but of a hypomanic state which cannot be regarded as psychotic."[37][38] Jung illustrated the hypomanic variation with five case histories, each involving hypomanic behaviour, occasional bouts of depression, and mixed mood states, which involved personal and interpersonal upheaval for each patient.[37]
In 1975, Jung's original distinction between mania and hypomania gained support. Fieve and Dunner published an article recognizing that only individuals in a manic state require hospitalization. It was proposed that the presentation of either the one state or the other differentiates two distinct diseases; the proposition was initially met with skepticism. However, studies since confirm that bipolar II is a "phenomenologically" distinct disorder.[8]
Empirical evidence, combined with treatment considerations, led the DSM-IV Mood Disorders Work Group to add bipolar II disorder as its own entity in the 1994 publication. (Only one other mood disorder was added to this edition, indicating the conservative nature of the DSM-IV work group.) In May 2013, the DSM-5 was released. Two revisions to the existing Bipolar II criteria are anticipated. The first expected change will reduce the required duration of a hypomanic state from four to two days. The second change will allow hypomania to be diagnosed without the manifestation of elevated mood;that is, increased energy/activity will be sufficient. The rationale behind the latter revision is that some individuals with Bipolar II manifest only visible changes in energy.  Without presenting elevated mood, these individuals are commonly misdiagnosed with major depressive disorder. Consequently, they receive prescriptions for antidepressants, which unaccompanied by mood stabilizers, may induce rapid cycling or mixed states.[39]
Society and culture

Maria Bamford has been diagnosed with Bipolar II.[40]
Heath Black revealed in his autobiography, Black, that he has been diagnosed with Bipolar II.[41]
Geoff Bullock, singer-songwriter, was diagnosed with Bipolar II.[42]
Mariah Carey was diagnosed with Bipolar II in 2001. In 2018, publicly revealed and actively seeking treatment in the form of therapy and medication.[43]
Charmaine Dragun, former Australian journalist/newsreader. Inquest concluded she had Bipolar II.[44]
Thomas Eagleton received a diagnosis of Bipolar II from Dr. Frederick K. Goodwin.[45]
Carrie Fisher had been diagnosed with Bipolar II.[46]
Shane Hmiel has been diagnosed with Bipolar II.[47]
Jesse Jackson Jr. has been diagnosed with Bipolar II.[48]
Albert Lasker is speculated to have had Bipolar II.[49]
Demi Lovato has been diagnosed with Bipolar II.[50][51]
Evan Perry, subject of the documentary Boy Interrupted, was diagnosed with Bipolar II.[52]
Richard Rossi, filmmaker, musician, and maverick minister was diagnosed with Bipolar II.[53]
Rumer has been diagnosed with Bipolar II.[54]
Robert Schumann is speculated to have had Bipolar II.[55]
Catherine Zeta-Jones received treatment for Bipolar II disorder after dealing with the stress of her husband's throat cancer. According to her publicist, Zeta-Jones made a decision to check into a "mental health facility" for a brief stay.[56]
Specifiers
Chronic
With Anxious Distress (DSM-5)
With catatonic features
With melancholic features
With psychotic features
With atypical features
With postpartum onset
Longitudinal course specifiers (with and without inter-episode recovery)
With seasonal pattern (applies only to the pattern of major depressive episodes)
With rapid cycling
See also
Bipolar disorder
Bipolar I disorder
Detailed listing of DSM-IV-TR bipolar disorder diagnostics codes
Bipolar spectrum
Cyclothymia
Emotional dysregulation
Creativity and bipolar disorder
Bipolar disorders research
Temporal lobe epilepsy

 via MedWorm.com


Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a common rock, is a combination of the minerals quartz, feldspar and biotite. The Earth's outer solid layer, the lithosphere, is made of rock.
Rock has been used by humankind throughout history. The minerals and metals in rocks have been essential to human civilization.[1]
Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology.
Classification

Rocks are composed of grains of minerals, which are homogeneous solids formed from a chemical compound arranged in an orderly manner.[2] The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which it was formed.
Many rocks contain silica (SiO2); a compound of silicon and oxygen that forms 74.3% of the Earth's crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their names and properties.[3]
Rocks are classified according to characteristics such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size. These physical properties are the result of the processes that formed the rocks.[4] Over the course of time, rocks can transform from one type into another, as described by a geological model called the rock cycle. This transformation produces three general classes of rock: igneous, sedimentary, and metamorphic.
Those three classes are subdivided into many groups. There are, however, no hard-and-fast boundaries between allied rocks. By increase or decrease in the proportions of their minerals, they pass through gradations from one to the other; the distinctive structures of one kind of rock may thus be traced gradually merging into those of another. Hence the definitions adopted in rock names simply correspond to selected points in a continuously graduated series.[5]
Igneous rock

Igneous rock (derived from the Latin word igneus, meaning of fire, from ignis meaning fire) is formed through the cooling and solidification of magma or lava. This magma may be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.
Igneous rocks are divided into two main categories:
Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust. A common example of this type is granite.
Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt.[4]
The chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowen's reaction series. Most major igneous rocks are found along this scale.[3]
About 64.7% of the Earth's crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, and 17% granodiorites and diorites. Only 0.6% are syenites and 0.3% peridotites and dunites. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Granites and similar rocks, known as meta-granitoids, form much of the continental crust.[6] Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and the temperature and pressure conditions in which they were formed.
Sedimentary rock

Sedimentary rocks are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms[7] or as chemical precipitates and organic growths in water (sedimentation). This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation at moderate temperatures and pressures (diagenesis).
Before being deposited, sediments are formed by weathering of earlier rocks by erosion in a source area and then transported to the place of deposition by water, wind, ice, mass movement or glaciers (agents of denudation). Mud rocks comprise 65% (mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone and dolostone).[4] About 7.9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consists of limestone (6%), sandstone and arkoses (12%).[6] Sedimentary rocks often contain fossils. Sedimentary rocks form under the influence of gravity and typically are deposited in horizontal or near horizontal layers or strata and may be referred to as stratified rocks. A small fraction of sedimentary rocks deposited on steep slopes will show cross bedding where one layer stops abruptly along an interface where another layer eroded the first as it was laid atop the first.
Metamorphic rock

Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization.[4] The temperatures and pressures required for this process are always higher than those found at the Earth's surface: temperatures greater than 150 to 200°C and pressures of 1500bars.[8] Metamorphic rocks compose 27.4% of the crust by volume.[6]
The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation. Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant, and temperature plays a smaller role. This is termed burial metamorphism, and it can result in rocks such as jade. Where both heat and pressure play a role, the mechanism is termed regional metamorphism. This is typically found in mountain-building regions.[3]
Depending on the structure, metamorphic rocks are divided into two general categories. Those that possess a texture are referred to as foliated; the remainders are termed non-foliated. The name of the rock is then determined based on the types of minerals present. Schists are foliated rocks that are primarily composed of lamellar minerals such as micas. A gneiss has visible bands of differing lightness, with a common example being the granite gneiss. Other varieties of foliated rock include slates, phyllites, and mylonite. Familiar examples of non-foliated metamorphic rocks include marble, soapstone, and serpentine. This branch contains quartzite—a metamorphosed form of sandstone—and hornfels.[3]
Human use

The use of rocks has had a huge impact on the cultural and technological development of the human race. Rocks have been used by humans and other hominids for at least 2.5million years.[9] Lithic technology marks some of the oldest and continuously used technologies. The mining of rocks for their metal ore content has been one of the most important factors of human advancement, which has progressed at different rates in different places in part because of the kind of metals available from the rocks of a region.
Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or (coal) seam.[10] This term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory. Mining in a wider sense comprises extraction of any resource (e.g. petroleum, natural gas, salt or even water) from the earth.[11]
Mining of rock and metals has been done since prehistoric times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials and finally reclamation of the land to prepare it for other uses once mining ceases.[12]
The nature of mining processes creates a potential negative impact on the environment both during the mining operations and for years after the mine has closed. This impact has led to most of the world's nations adopting regulations to manage negative effects of mining operations.[13]
See also

History of Earth
Geologic time scale
Geomorphology
Boulder
List of rock types
Oldest rock
Stone industry

Rocks at Wikibooks
 Media related to rocks at Wikimedia Commons
 The dictionary definition of rock at Wiktionary

What is the most common type of rock on Earth?


History of JapanEmperor Meiji moving from Kyoto to Tokyo, end of 1868, as imagined by Le Monde Illustre
ListPaleolithicbefore 14,000 BCJōmon14,000 – 300 BCYayoi300 BC – 300 ADKofun300–538Asuka538–710Nara710–794Heian794–1185Kamakura1185–1333Kenmu Restoration1333–1336Muromachi (Ashikaga)
Nanboku-chōSengoku 1336–1573Azuchi–Momoyama
Nanban trade 1573–1603Edo (Tokugawa)
SakokuConvention of KanagawaBakumatsu 1603–1868Meiji
Boshin WarRestorationFirst Sino-Japanese WarBoxer RebellionRusso-Japanese War 1868–1912Taishō
World War I 1912–1926Shōwa
Financial crisisMilitarismWorld War IIOccupationEconomic miraclePost-occupationBubble economy1926–1989Heisei
Lost DecadeGreat Hanshin earthquakeGreat East Japan earthquakeImperial transition 1989–2019Reiwa2019–present
Topics
Currency
Earthquakes
Economy
Education
Empire
Historiography
Military
Naval
Post-war

Glossary
Timelinevt
The Meiji Restoration(明治維新,Meiji Ishin), also known as the Meiji Renovation, Revolution, Reform, or Renewal, was an event that restored practical imperial rule to the Empire of Japan in 1868 under Emperor Meiji. Although there were ruling Emperors before the Meiji Restoration, the events restored practical abilities and consolidated the political system under the Emperor of Japan.
The goals of the restored government were expressed by the new Emperor in the Charter Oath. The Restoration led to enormous changes in Japan's political and social structure and spanned both the late Edo period (often called the Bakumatsu) and the beginning of the Meiji period.
Foreign influence
The Japanese knew that they were behind the Western world when American Commodore Matthew C. Perry came to Japan in 1853 in large warships with armament and technology that far outclassed those of Japan with the intent to conclude a treaty that would open up Japanese ports to trade.[1] Figures like Shimazu Nariakira concluded that "if we take the initiative, we can dominate; if we do not, we will be dominated", leading Japan to "throw open its doors to foreign technology." Observing Japan's response to the Western powers, Chinese general Li Hongzhang considered Japan to be China's "principal security threat" as early as 1863, five years before the Meiji Restoration.[2]
The leaders of the Meiji Restoration, as this revolution came to be known, acted in the name of restoring imperial rule to strengthen Japan against the threat represented by the colonial powers of the day, bringing to an end the era known as sakoku (the foreign relations policy, lasting about 250 years, prescribing the death penalty for foreigners entering or Japanese nationals leaving the country). The word "Meiji" means "enlightened rule" and the goal was to combine "modern advances" with traditional "eastern" values.[3] The main leaders of this were Itō Hirobumi, Matsukata Masayoshi, Kido Takayoshi, Itagaki Taisuke, Yamagata Aritomo, Mori Arinori, Ōkubo Toshimichi, and Yamaguchi Naoyoshi.
Imperial restoration
The foundation of the Meiji Restoration was the 1866 Satsuma-Chōshū Alliance between Saigō Takamori and Kido Takayoshi, leaders of the reformist elements in the Satsuma Domain and Chōshū Domain. These two leaders supported the Emperor Kōmei (Emperor Meiji's father) and were brought together by Sakamoto Ryōma for the purpose of challenging the ruling Tokugawa shogunate (bakufu) and restoring the Emperor to power. After Emperor Kōmei's death on January 30, 1867, Emperor Meiji ascended the throne on February 3. This period also saw Japan change from being a feudal society to having a market economy and left the Japanese with a lingering influence of Modernity.[4]
End of the shogunate

The Tokugawa government had been founded in the 17th century and initially focused on reestablishing order in social, political and international affairs after a century of warfare. The political structure, established by Ieyasu and solidified under his two immediate successors, his son Hidetada (who ruled from 1616–23) and grandson Iemitsu (1623–51), bound all daimyōs to the shogunate and limited any individual daimyō from acquiring too much land or power.[5] The Tokugawa shogunate came to its official end on November 9, 1867, when Tokugawa Yoshinobu, the 15th Tokugawa shōgun, "put his prerogatives at the Emperor's disposal" and resigned 10 days later.[6] This was effectively the "restoration" (Taisei Hōkan) of imperial rule – although Yoshinobu still had significant influence and it was not until January 3, the following year, with the young Emperor's edict, that the restoration fully occurred.[7]
Shortly thereafter in January 1868, the Boshin War (War of the Year of the Dragon) started with the Battle of Toba–Fushimi in which Chōshū and Satsuma's forces defeated the ex-shōgun's army. This forced (or allowed) the Emperor to strip Yoshinobu of all power, setting the stage for official restoration. On January 3, 1868, the Emperor made a formal declaration of the restoration of his power:
The Emperor of Japan announces to the sovereigns of all foreign countries and to their subjects that permission has been granted to the Shōgun Tokugawa Yoshinobu to return the governing power in accordance with his own request. We shall henceforward exercise supreme authority in all the internal and external affairs of the country. Consequently, the title of Emperor must be substituted for that of Taikun, in which the treaties have been made. Officers are being appointed by us to the conduct of foreign affairs. It is desirable that the representatives of the treaty powers recognize this announcement.—Mutsuhito, January 3, 1868[8]

All Tokugawa lands were seized and placed under "imperial control", thus placing them under the prerogative of the new Meiji government. With Fuhanken sanchisei, the areas were split into three types: urban prefectures(府,fu), rural prefectures(県,ken) and the already existing domains.
In 1869, the daimyōs of the Tosa, Hizen, Satsuma and Chōshū Domains, who were pushing most fiercely against the shogunate, were persuaded to "return their domains to the Emperor". Other daimyō were subsequently persuaded to do so, thus creating, arguably for the first time, a central government in Japan which exercised direct power through the entire "realm" (天下).
Some shogunate forces escaped to Hokkaidō, where they attempted to set up a breakaway Republic of Ezo; however, forces loyal to the Emperor ended this attempt in May 1869 with the Battle of Hakodate in Hokkaidō. The defeat of the armies of the former shōgun (led by Enomoto Takeaki and Hijikata Toshizō) marked the final end of the Tokugawa shogunate, with the Emperor's power fully restored.
Finally, by 1872, the daimyōs, past and present, were summoned before the Emperor, where it was declared that all domains were now to be returned to the Emperor. The roughly 280 domains were turned into 72 prefectures, each under the control of a state-appointed governor. If the daimyōs peacefully complied, they were given a prominent voice in the new Meiji government.[9] Later, their debts and payments of samurai stipends were either taxed heavily or turned in to bonds which resulted in a large loss of wealth among former samurai.[10]
Military reform

The Meiji Emperor announced in his 1868 Charter Oath that "Knowledge shall be sought all over the world, and thereby the foundations of imperial rule shall be strengthened."[2]
Under the leadership of Mori Arinori, a group of prominent Japanese intellectuals went on to form the Meiji Six Society in 1873 to continue to "promote civilization and enlightenment" through modern ethics and ideas. However, during the restoration, political power simply moved from the Tokugawa shogunate to an oligarchy consisting of these leaders, mostly from Satsuma Province (Ōkubo Toshimichi and Saigō Takamori), and Chōshū Province (Itō Hirobumi, Yamagata Aritomo, and Kido Takayoshi). This reflected their belief in the more traditional practice of imperial rule, whereby the Emperor of Japan serves solely as the spiritual authority of the nation and his ministers govern the nation in his name.
The Meiji oligarchy that formed the government under the rule of the Emperor first introduced measures to consolidate their power against the remnants of the Edo period government, the shogunate, daimyōs, and the samurai class. The oligarchs also endeavored to abolish the four divisions of society.

Throughout Japan at the time, the samurai numbered 1.9 million. (For comparison, this was more than 10 times the size of the French privileged class before the 1789 French Revolution. Moreover, the samurai in Japan were not merely the lords, but also their higher retainers—people who actually worked.) With each samurai being paid fixed stipends, their upkeep presented a tremendous financial burden, which may have prompted the oligarchs to action.
Whatever their true intentions, the oligarchs embarked on another slow and deliberate process to abolish the samurai class. First, in 1873, it was announced that the samurai stipends were to be taxed on a rolling basis. Later, in 1874, the samurai were given the option to convert their stipends into government bonds. Finally, in 1876, this commutation was made compulsory.
To reform the military, the government instituted nationwide conscription in 1873, mandating that every male would serve for four years in the armed forces upon turning 21 years old, followed by three more years in the reserves. One of the primary differences between the samurai and peasant classes was the right to bear arms; this ancient privilege was suddenly extended to every male in the nation. Furthermore, samurai were no longer allowed to walk about town bearing a sword or weapon to show their status.
This led to a series of riots from disgruntled samurai. One of the major riots was the one led by Saigō Takamori, the Satsuma Rebellion, which eventually turned into a civil war. This rebellion was, however, put down swiftly by the newly formed Imperial Japanese Army, trained in Western tactics and weapons, even though the core of the new army was the Tokyo police force, which was largely composed of former samurai. This sent a strong message to the dissenting samurai that their time was indeed over. There were fewer subsequent samurai uprisings and the distinction became all but a name as the samurai joined the new society. The ideal of samurai military spirit lived on in romanticized form and was often used as propaganda during the early 20th-century wars of the Empire of Japan.
However, it is equally true that the majority of samurai were content despite having their status abolished. Many found employment in the government bureaucracy, which resembled an elite class in its own right. The samurai, being better educated than most of the population, became teachers, gun makers, government officials, and/or military officers. While the formal title of samurai was abolished, the elitist spirit that characterized the samurai class lived on.
The oligarchs also embarked on a series of land reforms. In particular, they legitimized the tenancy system which had been going on during the Tokugawa period. Despite the bakufu's best efforts to freeze the four classes of society in place, during their rule villagers had begun to lease land out to other farmers, becoming rich in the process. This greatly disrupted the clearly defined class system which the bakufu had envisaged, partly leading to their eventual downfall.
The military of Japan, being strengthened by nationwide conscription and the infusion of a samurai military spirit, became emboldened to see themselves as a growing world power after winning both the Sino-Japanese War and the Russo-Japanese War.
Centralization
Besides drastic changes to the social structure of Japan, in an attempt to create a strong centralized state defining its national identity, the government established a dominant national dialect, called "standard language"(標準語,hyōjungo), that replaced local and regional dialects and was based on the patterns of Tokyo's samurai classes. This dialect eventually became the norm in the realms of education, media, government, and business.[11]
The Meiji Restoration, and the resultant modernization of Japan, also influenced Japanese self-identity with respect to its Asian neighbours, as Japan became the first Asian state to modernize based on the Western model, replacing the traditional Confucian hierarchical order that had persisted previously under a dominant China with one based on modernity.[12]
Industrial growth
The Meiji Restoration accelerated industrialization in Japan, which led to its rise as a military power by the year 1895, under the slogan of "Enrich the country, strengthen the military"(富国強兵,fukoku kyōhei).
Japan's economic powers are a major influence on the industrial factor of its country as well. Economics and market are both influenced how the people used the market as a place of growth. The nation of Japan had gone under a mass transformation that helped them economically. Japan had help from Western nations when it came to the industrial growth. This is important to the growth and ideas that came with the reforms and transformation Japan was undergoing during the Meiji period.
During the Meiji period powers such as Europe and the United States helped transform Japan and made them realize a change needed to take place. Some leaders went out to foreign lands and used the knowledge and government writings to help shape and form a more influential government within their walls that allowed for things such as production. Despite the help Japan received from other powers, one of the key factors in Japan's industrializing success was its relative lack of resources, which made it unattractive to Western imperialism.[13] The farmer and the samurai classification were the base and soon the problem of why there was a limit of growth within the nation's industrial work. The government sent officials such as the samurai to monitor the work that was being done. Because of Japan's leaders taking control and adapting Western techniques it has remained one of the world’s largest industrial nations.
The rapid industrialization and modernization of Japan both allowed and required a massive increase in production and infrastructure. Japan built industries such as shipyards, iron smelters, and spinning mills, which were then sold to well-connected entrepreneurs. Consequently, domestic companies became consumers of Western technology and applied it to produce items that would be sold cheaply in the international market. With this, industrial zones grew enormously, and there was a massive migration to industrializing centers from the countryside. Industrialization additionally went hand in hand with the development of a national railway system and modern communications.[14]

With industrialization came the demand for coal. There was dramatic rise in production, as shown in the table below.

Coal was needed for steamships and railroads. The growth of these sectors is shown below.

See also
Bakumatsu
Datsu-A Ron
Land Tax Reform (Japan 1873)
Modernization of Japanese Military 1868–1931
Meiji Constitution
Four Hitokiri of the Bakumatsu
Gwangmu Reform, the similar process in neighboring Korea
Notes
1. Although the political system was consolidated under the Emperor of Japan, power was mainly transferred to a group of people, known as the Meiji oligarchy (and Genrō), who helped in the restoration of imperial power.[10]

Further reading

CS1 maint: Extra text: authors list (link)

Breen, John, 'The Imperial Oath of April 1868: ritual, power and politics in Restoration Japan', Monumenta Nipponica,51,4 (1996)
Francisco Barberan & Rafael Domingo Osle, Codigo civil japones. Estudio preliminar, traduccion y notas (2 ed. Thomsons Aranzadi, 2006).
Harry D. Harootunian, Toward Restoration (Berkeley: University of California Press, 1970), "Introduction", pp 1 – 46; on Yoshida: chapter IV "The Culture of Action – Yoshida Shōin", pp 184 – 219.
Najita Tetsuo, The Intellectual Foundations of Modern Japanese Politics (Chicago & London: University of Chicago Press), chapter 3: "Restorationism in Late Tokugawa", pp 43 – 68.
H. Van Straelen, Yoshida Shōin, Forerunner of the Meiji Restoration: A Biographical Study (Leiden: E. J. Brill, 1952).
David M. Earl, Emperor and Nation in Japan (Seattle: University of Washington Press, 1972), on Yoshida: "Attitude toward the Emperor/Nation", pp 161 – 192. Also pp.82 – 105.
Marius B Jansen, Sakamoto Ryōma and the Meiji Restoration (New York: Columbia University Press, 1994) especially chapter VIII: "Restoration", pp 312 – 346.
W. G. Beasley, The Meiji Restoration (Stanford, California: Stanford University Press, 1972), especially chapter VI: "Dissenting Samurai", pp 140 – 171.
Conrad Totman, "From Reformism to Transformism, bakufu Policy 1853–1868", in: T. Najita & V. J. Koshmann, Conflict in Modern Japanese History (New Jersay: Princeton University Press, 1988), pp.62 – 80.
Jansen, Marius B.: The Meiji Restoration, in: Jansen, Marius B. (ed.): The Cambridge history of Japan, Volume 5: The nineteenth century (New York: Cambridge UP, 1989), pp.308–366.
Robert W. Strayer, Ways of the World with Sources Vol. 2 (2nd ed.), pp 950 (2013)

 on the About Japan, A Teacher's Resource website
 from famous 19th-century Japanese and European photographers

What or who was the Meiji Restoration named for?


Earth's oceans
Arctic
Atlantic
Indian
Pacific
Southern
World Oceanvt
The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south and is bounded by Asia and Australia in the west and the Americas in the east.
At 165,250,000 square kilometers (63,800,000 square miles) in area (as defined with an Antarctic southern border), this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined.[1] The centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific.[2] Its mean depth is 4,000 meters (13,000 feet)[3]. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters (35,797 feet).[4] The western Pacific has many peripheral seas.
Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times, the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur (in Spanish). The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means "peaceful sea".[5]
History
Early migrations

Important human migrations occurred in the Pacific in prehistoric times. About 3000BC, the Austronesian peoples on the island of Taiwan mastered the art of long-distance canoe travel and spread themselves and their languages south to the Philippines, Indonesia, and maritime Southeast Asia; west towards Madagascar; southeast towards New Guinea and Melanesia (intermarrying with native Papuans); and east to the islands of Micronesia, Oceania and Polynesia.[7]
Long-distance trade developed all along the coast from Mozambique to Japan. Trade, and therefore knowledge, extended to the Indonesian islands but apparently not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean.
European exploration

The first contact of European navigators with the western edge of the Pacific Ocean was made by the Portuguese expeditions of António de Abreu and Francisco Serrão, via the Lesser Sunda Islands, to the Maluku Islands, in 1512,[8][9] and with Jorge Álvares's expedition to southern China in 1513,[10] both ordered by Afonso de Albuquerque from Malacca.
The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean.[11] He named it Mar del Sur (literally, "Sea of the South" or "South Sea") because the ocean was to the south of the coast of the isthmus where he first observed the Pacific.

In 1519, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Spanish expedition to the Spice Islands that would eventually result in the first world circumnavigation. Magellan called the ocean Pacífico (or "Pacific" meaning, "peaceful") because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters. The ocean was often called the Sea of Magellan in his honor until the eighteenth century.[12] Although Magellan himself died in the Philippines in 1521, Spanish Basque navigator Juan Sebastián Elcano led the remains of the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in a single expedition in 1522.[13] Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands,[14] the Aru Islands,[15] and Papua New Guinea.[16] In 1542–43 the Portuguese also reached Japan.[17]
In 1564, five Spanish ships carrying 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi, and sailed to the Philippines and Mariana Islands.[18] For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Mexico and Peru across the Pacific Ocean to the Philippines via Guam, and establishing the Spanish East Indies. The Manila galleons operated for two and a half centuries, linking Manila and Acapulco, in one of the longest trade routes in history. Spanish expeditions also discovered Tuvalu, the Marquesas, the Cook Islands, the Solomon Islands, and the Admiralty Islands in the South Pacific.[19]
Later, in the quest for Terra Australis ("the [great] Southern Land"), Spanish explorations in the 17th century, such as the expedition led by the Portuguese navigator Pedro Fernandes de Queirós, discovered the Pitcairn and Vanuatu archipelagos, and sailed the Torres Strait between Australia and New Guinea, named after navigator Luís Vaz de Torres. Dutch explorers, sailing around southern Africa, also engaged in discovery and trade; Willem Janszoon, made the first completely documented European landing in Australia (1606), in Cape York Peninsula,[20] and Abel Janszoon Tasman circumnavigated and landed on parts of the Australian continental coast and discovered Tasmania and New Zealand in 1642.[21]
In the 16th and 17th centuries Spain considered the Pacific Ocean a mare clausum—a sea closed to other naval powers. As the only known entrance from the Atlantic, the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western side of the Pacific Ocean the Dutch threatened the  Spanish Philippines.[22]
The 18th century marked the beginning of major exploration by the Russians in Alaska and the Aleutian Islands, such as the First Kamchatka expedition and the Great Northern Expedition, led by the Danish Russian navy officer Vitus Bering. Spain also sent expeditions to the Pacific Northwest, reaching Vancouver Island in southern Canada, and Alaska. The French explored and settled Polynesia, and the British made three voyages with James Cook to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest. In 1768, Pierre-Antoine Véron, a young astronomer accompanying Louis Antoine de Bougainville on his voyage of exploration, established the width of the Pacific with precision for the first time in history.[23] One of the earliest voyages of scientific exploration was organized by Spain in the Malaspina Expedition of 1789–1794. It sailed vast areas of the Pacific, from Cape Horn to Alaska, Guam and the Philippines, New Zealand, Australia, and the South Pacific.[19]
New Imperialism

Growing imperialism during the 19th century resulted in the occupation of much of Oceania by European powers, and later Japan and the United States. Significant contributions to oceanographic knowledge were made by the voyages of HMS Beagle in the 1830s, with Charles Darwin aboard;[24] HMS Challenger during the 1870s;[25] the USS Tuscarora (1873–76);[26] and the German Gazelle (1874–76).[27]

In Oceania, France obtained a leading position as imperial power after making Tahiti and New Caledonia protectorates in 1842 and 1853 respectively.[28] After navy visits to Easter Island in 1875 and 1887, Chilean navy officer Policarpo Toro negotiated the incorporation of the island into Chile with native Rapanui in 1888. By occupying Easter Island, Chile joined the imperial nations.[29](p53) By 1900 nearly all Pacific islands were in control of Britain, France, United States, Germany, Japan, and Chile.[28]
Although the United States gained control of Guam and the Philippines from Spain in 1898,[30] Japan controlled most of the western Pacific by 1914 and occupied many other islands during World War II. However, by the end of that war, Japan was defeated and the U.S. Pacific Fleet was the virtual master of the ocean. Since the end of World War II, many former colonies in the Pacific have become independent states.
Geography

The Pacific separates Asia and Australia from the Americas. It may be further subdivided by the equator into northern (North Pacific) and southern (South Pacific) portions. It extends from the Antarctic region in the South to the Arctic in the north.[1] The Pacific Ocean encompasses approximately one-third of the Earth's surface, having an area of 165,200,000km2 (63,800,000sqmi)—significantly larger than Earth's entire landmass of some 150,000,000km2 (58,000,000sqmi).[31]
Extending approximately 15,500km (9,600mi) from the Bering Sea in the Arctic to the northern extent of the circumpolar Southern Ocean at 60°S (older definitions extend it to Antarctica's Ross Sea), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800km (12,300mi) from Indonesia to the coast of Colombia—halfway around the world, and more than five times the diameter of the Moon.[32] The lowest known point on Earth—the Mariana Trench—lies 10,911m (35,797ft; 5,966 fathoms) below sea level. Its average depth is 4,280m (14,040ft; 2,340 fathoms), putting the total water volume at roughly 710,000,000km3 (170,000,000cumi).[1]
Due to the effects of plate tectonics, the Pacific Ocean is currently shrinking by roughly 2.5cm (1in) per year on three sides, roughly averaging 0.52km2 (0.20sqmi) a year. By contrast, the Atlantic Ocean is increasing in size.[33][34]
Along the Pacific Ocean's irregular western margins lie many seas, the largest of which are the Celebes Sea, Coral Sea, East China Sea (East Sea), Philippine Sea, Sea of Japan, South China Sea (South Sea), Sulu Sea, Tasman Sea, and Yellow Sea (West Sea of Korea). The Indonesian Seaway (including the Strait of Malacca and Torres Strait) joins the Pacific and the Indian Ocean to the west, and Drake Passage and the Strait of Magellan link the Pacific with the Atlantic Ocean on the east. To the north, the Bering Strait connects the Pacific with the Arctic Ocean.[35]
As the Pacific straddles the 180th meridian, the West Pacific (or western Pacific, near Asia) is in the Eastern Hemisphere, while the East Pacific (or eastern Pacific, near the Americas) is in the Western Hemisphere.[36]
The Southern Pacific Ocean harbors the Southeast Indian Ridge crossing from south of Australia turning into the Pacific-Antarctic Ridge (north of the South Pole) and merges with another ridge (south of South America) to form the East Pacific Rise which also connects with another ridge (south of North America) which overlooks the Juan de Fuca Ridge.
For most of Magellan's voyage from the Strait of Magellan to the Philippines, the explorer indeed found the ocean peaceful. However, the Pacific is not always peaceful. Many tropical storms batter the islands of the Pacific.[37]  The lands around the Pacific Rim are full of volcanoes and often affected by earthquakes.[38] Tsunamis, caused by underwater earthquakes, have devastated many islands and in some cases destroyed entire towns.[39]
The Martin Waldseemüller map of 1507 was the first to show the Americas separating two distinct oceans.[40] Later, the Diogo Ribeiro map of 1529 was the first to show the Pacific at about its proper size.[41]
Bordering countries and territories

Sovereign nations

Australia
Brunei
Cambodia
Canada
Chile
China1
Colombia
Costa Rica
Ecuador
El Salvador
Federated States of Micronesia
Fiji
Guatemala
Honduras
Indonesia
Japan
Kiribati
North Korea
South Korea
Malaysia
Marshall Islands
Mexico
Nauru
Nicaragua
New Zealand
Palau
Panama
Papua New Guinea
Peru
Philippines
Russia
Samoa
Singapore
Solomon Islands
Taiwan1
Thailand
Timor-Leste
Tonga
Tuvalu
United States
Vanuatu
Vietnam

1 The status of Taiwan and China is disputed. For more information, see political status of Taiwan.
Territories

American Samoa (US)
 Baker Island (US)
 Clipperton Island (France)
Cook Islands (New Zealand)
 Coral Sea Islands (Australia)
Easter Island (Chile)
French Polynesia (France)
Guam (US)
Hong Kong (China)
 Howland Island (US)
 Jarvis Island (US)
 Johnston Island (US)
 Kingman Reef (US)
Macau (China)
 Midway Atoll (US)
New Caledonia (France)
Niue (New Zealand)
Norfolk Island (Australia)
Northern Mariana Islands (US)
 Palmyra Atoll (US)
Pitcairn Islands (UK)
Tokelau (New Zealand)
Wallis and Futuna (France)
 Wake Island (US)

Landmasses and islands

This ocean has most of the islands in the world. There are about 25,000 islands in the Pacific Ocean.[42][43][44] The islands entirely within the Pacific Ocean can be divided into three main groups known as Micronesia, Melanesia and Polynesia. Micronesia, which lies north of the equator and west of the International Date Line, includes the Mariana Islands in the northwest, the Caroline Islands in the center, the Marshall Islands to the west and the islands of Kiribati in the southeast.[45][46]
Melanesia, to the southwest, includes New Guinea, the world's second largest island after Greenland and by far the largest of the Pacific islands. The other main Melanesian groups from north to south are the Bismarck Archipelago, the Solomon Islands, Santa Cruz, Vanuatu, Fiji and New Caledonia.[47]
The largest area, Polynesia, stretching from Hawaii in the north to New Zealand in the south, also encompasses Tuvalu, Tokelau, Samoa, Tonga and the Kermadec Islands to the west, the Cook Islands, Society Islands and Austral Islands in the center, and the Marquesas Islands, Tuamotu, Mangareva Islands, and Easter Island to the east.[48]
Islands in the Pacific Ocean are of four basic types: continental islands, high islands, coral reefs and uplifted coral platforms. Continental islands lie outside the andesite line and include New Guinea, the islands of New Zealand, and the Philippines. Some of these islands are structurally associated with nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands.[49]
The coral reefs of the South Pacific are low-lying structures that have built up on basaltic lava flows under the ocean's surface. One of the most dramatic is the Great Barrier Reef off northeastern Australia with chains of reef patches. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Examples include Banaba (formerly Ocean Island) and Makatea in the Tuamotu group of French Polynesia.[50][51]

Ladrilleros Beach in Colombia on the coast of Chocó natural region
Point Reyes headlands, Point Reyes National Seashore, California
Tahuna maru islet, French Polynesia
Los Molinos on the coast of Southern Chile

Water characteristics

The volume of the Pacific Ocean, representing about 50.1 percent of the world's oceanic water, has been estimated at some 714million cubic kilometers (171million cubic miles).[52] Surface water temperatures in the Pacific can vary from −1.4°C (29.5°F), the freezing point of sea water, in the poleward areas to about 30°C (86°F) near the equator.[53] Salinity also varies latitudinally, reaching a maximum of 37 parts per thousand in the southeastern area. The water near the equator, which can have a salinity as low as 34 parts per thousand, is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. The lowest counts of less than 32 parts per thousand are found in the far north as less evaporation of seawater takes place in these frigid areas.[54] The motion of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.[55]
Turning eastward at about 45°N, the Kuroshio forks and some water moves northward as the Aleutian Current, while the rest turns southward to rejoin the North Equatorial Current.[56] The Aleutian Current branches as it approaches North America and forms the base of a counter-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled slow, south-flowing California Current.[57] The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50°S, and joins the main westerly circulation of the South Pacific, which includes the Earth-circling Antarctic Circumpolar Current. As it approaches the Chilean coast, the South Equatorial Current divides; one branch flows around Cape Horn and the other turns north to form the Peru or Humboldt Current.[58]
Climate

The climate patterns of the Northern and Southern Hemispheres generally mirror each other. The trade winds in the southern and eastern Pacific are remarkably steady while conditions in the North Pacific are far more varied with, for example, cold winter temperatures on the east coast of Russia contrasting with the milder weather off British Columbia during the winter months due to the preferred flow of ocean currents.[59]
In the tropical and subtropical Pacific, the El Niño Southern Oscillation (ENSO) affects weather conditions.  To determine the phase of ENSO, the most recent three-month sea surface temperature average for the area approximately 3,000km (1,900mi) to the southeast of Hawaii is computed, and if the region is more than 0.5°C (0.9°F) above or below normal for that period, then an El Niño or La Niña is considered in progress.[60]
In the tropical western Pacific, the monsoon and the related wet season during the summer months contrast with dry winds in the winter which blow over the ocean from the Asian landmass.[61]  Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are active.[62]  The Pacific hosts the two most active tropical cyclone basins, which are the northwestern Pacific and the eastern Pacific. Pacific hurricanes form south of Mexico, sometimes striking the western Mexican coast and occasionally the southwestern United States between June and October, while typhoons forming in the northwestern Pacific moving into southeast and east Asia from May to December. Tropical cyclones also form in the South Pacific basin, where they occasionally impact island nations.
In the arctic, icing from October to May can present a hazard for shipping while persistent fog occurs from June to December.[63]  A climatological low in the Gulf of Alaska keeps the southern coast wet and mild during the winter months.  The Westerlies and associated jet stream within the Mid-Latitudes can be particularly strong, especially in the Southern Hemisphere, due to the temperature difference between the tropics and Antarctica,[64] which records the coldest temperature readings on the planet.  In the Southern hemisphere, because of the stormy and cloudy conditions associated with extratropical cyclones riding the jet stream, it is usual to refer to the Westerlies as the Roaring Forties, Furious Fifties and Shrieking Sixties according to the varying degrees of latitude.[65]
Geology

The ocean was first mapped by Abraham Ortelius; he called it Maris Pacifici following Ferdinand Magellan's description of it as "a pacific sea" during his circumnavigation from 1519 to 1522. To Magellan, it seemed much more calm (pacific) than the Atlantic.[66]
The andesite line is the most significant regional distinction in the Pacific. A petrologic boundary, it separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins.[67] The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island.[68][69]
The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand lie outside the andesite line.
Within the closed loop of the andesite line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. Here basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the andesite line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism.[45] The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones.
The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.
Geological history
The Pacific Ocean was born 750 million years ago at the breakup of Rodinia, although it is generally called the Panthalassic Ocean until the breakup of  Pangea, about 200 million years ago.[70] The oldest Pacific Ocean floor is only around 180 Ma old, with older crust subducted by now.[71]
Seamount chains
The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Hawaiian–Emperor seamount chain and the Louisville Ridge.
Economy
The exploitation of the Pacific's mineral wealth is hampered by the ocean's great depths. In shallow waters of the continental shelves off the coasts of Australia and New Zealand, petroleum and natural gas are extracted, and pearls are harvested along the coasts of Australia, Japan, Papua New Guinea, Nicaragua, Panama, and the Philippines, although in sharply declining volume in some cases.[72]
Fishing
Fish are an important economic asset in the Pacific. The shallower shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish.[73] Overfishing has become a serious problem in some areas. For example, catches in the rich fishing grounds of the Okhotsk Sea off the Russian coast have been reduced by at least half since the 1990s as a result of overfishing.[74]
Environmental issues

The quantity of small plastic fragments floating in the north-east Pacific Ocean increased a hundredfold between 1972 and 2012.[75]
Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The main culprits are those using the rivers for disposing of their waste.[76] The rivers then empty into the ocean, often also bringing chemicals used as fertilizers in agriculture. The excess of oxygen-depleting chemicals in the water leads to hypoxia and the creation of a dead zone.[77]
Marine debris, also known as marine litter, is human-created waste that has ended up floating in a lake, sea, ocean, or waterway. Oceanic debris tends to accumulate at the center of gyres and coastlines, frequently washing aground where it is known as beach litter.[76]
In addition, the Pacific Ocean has served as the crash site of satellites, including Mars 96, Fobos-Grunt, and Upper Atmosphere Research Satellite.
Major ports and harbors

See also

Asia-Pacific Economic Cooperation
Pacific Alliance
Pacific coast
Pacific Time Zone
Pacific War
Seven Seas
Trans-Pacific Partnership
War of the Pacific

Further reading

CS1 maint: extra text: authors list (link)

Paine, Lincoln. The Sea and Civilization: A Maritime History of the World (2015).

Samson, Jane. British imperial strategies in the Pacific, 1750–1900 (Ashgate Publishing, 2003).

Historiography
Davidson, James Wightman. "Problems of Pacific history." Journal of Pacific History 1#1 (1966): 5–21.
Gulliver, Katrina. "Finding the Pacific world." Journal of World History 22#1 (2011): 83–100.

Munro, Doug. The Ivory Tower and Beyond: Participant Historians of the Pacific (Cambridge Scholars Publishing, 2009).
Routledge, David. "Pacific history as seen from the Pacific Islands." Pacific Studies 8#2 (1985): 81+
Samson, Jane. "Pacific/Oceanic History" in CS1 maint: extra text: authors list (link)

 on-line collection of observational data
 plot and download ocean observations

 El Niño data Realtime Pacific Ocean El Niño buoy data
 – Realtime (OSCAR) Near-realtime Pacific Ocean Surface Currents derived from satellite altimeter and scatterometer data

What is the surface area of the Pacific Ocean in cubic meters?