The Bible does not say that the Earth is only six thousand years old. What the Bible does indicate and record is that Adam and Eve were created approximately six thousand years ago (via the genealogies with lists of Adam's descendants and ages). Prior to the creation of Adam and Eve, going back perhaps thousands and millions of years, life existed in previous ages on the Earth. At some point, as indicated by the Bible, this life was destroyed in a great cataclysm, including flooding by water. Genesis 1:2 records that the Creator "moved upon the face of the waters" of this desolated Earth, and then "remade" the Earth and re-created life on the Earth.
This all can be shown from a proper translation of Genesis and other passages in the Bible from the original Hebrew and Greek.
Hebrew and Greek Lexicon
Source: Bible Study Site: "When Was The Beginning?"
[NOTE/DISCLAMER: I am unsure about some of the teaching in the above source (eg, the claim that the one third of the "stars of heaven" who revolted with Lucifer included our own souls in spiritual bodies in this previous age), and therefore do not endorse the source in full. ]
Excerpts from source:
Embedded notes in Scripture (by #):
*1). In the beginning. It states: "In the beginning," but it doesn't say when that was. We know from archeology that this earth is billions of years old. Scientific Carbon Dating does not contradict this verse!
There is no date given in the above Scripture, why try to affix one? It is impossible, for there is no reference point given. We can however pick up a date when Adam will later in the Scriptures be formed, because all his ancestor's ages are given in the Scriptures themselves, and the age that they were when they had the next child chronologically in the list. There was a reason that God saw to it that this, seemingly redundant and unimportant information, was handed down through the Millennia whereby we may simply add the numbers up together and deduct them from any certain date in secular history.
But Adam's being formed is long after this verse transpires. This is a substantial point often overlooked by those whom, for whatever reasons of their own, seek to cast doubt on the Bible. It didn't say that God created the Earth when He formed Adam. So while with certainly we may date Adam, we cannot do the same with the date of the creation of the world. Why charge God and His Bible with error when the real problem is our inability to read what is written and to not read into it that which is not written?
*2). We notice that there is a period at the end of this sentence. That means that this thought is complete and the next sentence is a new thought. In reality there is unknown eons of time between this verse and the next. This is what is called time gap in scriptures, and it is recognized to occur in at least twenty-five places in the Bible.
Using Strong's Concordance for Genesis 1:2, we get the following:
"And the earth [H776] was [H1961] (8804) without form [H8414], and void [H922]; and darkness [H2822] [was] upon the face [H6440] of the deep [H8415]. And the Spirit [H7307] of God [H430] moved [H7363] (8764) upon [H5921] the face [H6440] of the waters [H4325]."
1). was is the English translation of a Hebrew word (hayah) which means Became. In other words, the earth was not created without form and void, but that it became that way at some point in time after it was created.
Hebrew word #1961 hayah (haw-yaw); a primitive root [compare 1933]; to exist, i.e. be or become, come to pass (always emphatic, and not a mere copula or auxiliary)
*2). without form was translated from the Hebrew word (tohuw) that means: to lie waste, a desolation. You cannot lie waste or desolate something unless it was once in good condition and then at some later time it was destroyed.
Hebrew word #8414 tohuw (to'-hoo);
from an unused root meaning to lie waste; a desolation (of surface), i.e. desert; figuratively, a worthless thing; adverbially, in vain: KJV-- confusion, empty place, without form, nothing, (thing of) nought, vain, vanity, waste, wilderness.
*3). void is translated from a Hebrew word (bohuw) that means: an indistinguishable ruin. You cannot have a ruin unless there was at first, something to ruin.
Hebrew word #922 bohuw (bo'-hoo);
from an unused root (meaning to be empty); a vacuity, i.e. (superficially) an undistinguishable ruin: KJV-- emptiness, void.
*4). darkness (choshek) as it is used here means to become dark, to be darkened. You cannot darken something that was not lit in the first place.
Hebrew word #2822 choshek (kho-shek');
from 2821; the dark; hence (literally) darkness; figuratively, misery, destruction, death, ignorance, sorrow, wickedness: KJV-- dark (-ness), night, obscurity.
*5). deep, this corresponds with the description of the destruction of the first earth age by water (NOT Noah's flood here).
Hebrew word #8415 tehowm (teh-home'); or tehom (teh-home');
(usually feminine) from 1949; an abyss (as a surging mass of water), especially the deep (the main sea or the subterranean water-supply): KJV-- deep (place), depth.
*6). There is a period at the end of this sentence. The following sentence marks the beginning of the rejuvenation into this (our current day) earth age.
*7). Spirit of God = The Holy Spirit; the Spirit of God IS the Holy Spirit.
Below, we will see what Almighty God says about the way He created the world, and we see that He did not create it void and without form, but that it became like that at a later time:
For thus saith the LORD that created the heavens; God himself that formed the earth and made it; he hath established it, he created it not in vain*1, he formed it to be inhabited: I am the LORD; and there is none else. (KJV)
*1). vain = There is something remarkable here that is lost to the English reader of the Bible. In the Hebrew Manuscripts that the above verse was translated out of, the word translated into the English as vain is translated from the identical Hebrew word that we saw in Gen 1:1 (tohuw - #2 above), it's the same Hebrew word.
So that should explain what it is really saying when we read in Gen 1:2: "And the earth was without form [tohuw], and void; and darkness was upon the face of the deep."
It is important to point out that the separation of Chapters, Verses, Sentences, and even the spaces between words is the work of the Scribes and the Translators. In the ancient Manuscripts, the whole page is written like one long word. The Scribes and Translators only had their interpretation of the meaning of the scripture to use as a guide, when separating Chapters, Verses, Lines, and the words.
This happens in our verse 2 above, in the middle of verse two after the period we have the sentence that marks the beginning of the rejuvenation of the world into our present earth age (the second of three): "And the Spirit of God moved upon the face of the waters." This rejuvenation continues on in the following verses as God creates everything as we know it in our world.
So therefore, with the truest meanings of the key defined words in the above scripture explained, we can thus take the first verse and the first half of the second verse, up to the period, and present it as such:
1) In the beginning God created the heaven and the earth.
2) And the earth was without form, and void; and darkness was upon the face of the deep. (Notice the periods)
And now we will explain the verse, not retranslate it. We will describe it so that it explains not only the Hebrew words in the English language, but also the Hebrew thought into the English understanding. Therefore, it will be better understood if read as:
In the beginning of time, when that was isn't stated, God created everything in the Heavens and on the earth. Then some unknown length of time later, something catastrophic occurred that made God's Creation come to utter destruction, it became a wasted place. This destruction manifested itself among other things as a total flood. So complete was this destructive event that not only did the earth become an indistinguishable ruin, but even the sun stopped shining its light upon it, and all the earth was cast into utter darkness.
Then the second sentence of verse 2 marks the start of the rejuvenation of the earth and the commencement of God's Creation on the earth as we know it now in this present second earth age which we now live in.
MORE SCRIPTURAL EVIDENCE OF THE DESTRUCTION OF THE EARTH IN A PREVIOUS AGE
2 Pet 3:5-7
5 For this they willingly are ignorant of, that by the word of God the heavens were of old, and the earth standing out of the water and in the water:
6 Whereby the world that then was, being overflowed with water, perished:
7 But the heavens and the earth, which are now, by the same word are kept in store, reserved unto fire against the day of judgment and perdition of ungodly men.
The above passage is not talking about the flood of Noah's time (which was not a worldwide flood anyway), because the world did not perish at that time (ie, Noah and his family survived, as well as plant life, etc).
Earth's Age: Does the Bible Indicate a Time Interval Between the First and Second Verses of Genesis?