The Oldest Homo Sapiens
Edited from the University of Utah Public Relations, 16 February
2005. Updated 8 February 2017
When the bones of two early humans were found in 1967
near Kibish, Ethiopia, they were thought to be 130,000 years old. Towards
the end of the twenty-first century, researchers found 154,000 to 160,000
year-old human bones at Herto, Ethiopia.
In 2005, a new study of the 1967 fossil site indicated
that the earliest known members of Homo sapiens roamed Africa about
195,000 years ago. 
Geologist Frank Brown, a co-author of the study and
dean of the University of Utah's College of Mines and Earth Sciences,
was of the opinion that it pushed back the start date for anatomically
modern humans. Published in the journal Nature on 17 February 2005,
Brown conducted the research with geologist and geochronologist Ian
McDougall of the Australian National University in Canberra, and
anthropologist John Fleagle of New York state's Stony Brook University,
The researchers dated mineral crystals in volcanic ash
layers above and below layers of river sediments that contained the early
human bones. They concluded that the fossils were much older than a
104,000 year-old volcanic layer and very close in age to a 196,000
year-old layer. At the time - 2005 - they were the oldest well-dated
fossils of modern humans (Homo sapiens) known anywhere in the
The significance of an earlier Homo sapiens
Pushing back the emergence of Homo sapiens
from about 160,000 years ago to about 195,000 years ago was significant
because the cultural aspects of humanity in most cases appear much
later in the record - only 50,000 years ago - which would mean
150,000 years of Homo sapiens without cultural materials, such as
evidence of eating fish, of harpoons, anything to do with music
(flutes and other musical instruments), needles, and even tools.
Such developments all came in very late, except for
stone knife blades which appeared between 50,000 and 200,000 years ago,
depending on which archaeologist you believe.
There was (and still is) a huge debate in archaeological
literature regarding the first appearance of modern aspects of
behaviour, such as bone carving for religious reasons, or tools
(harpoons and other items), ornamentation (bead jewellery, for example),
drawn images, or arrowheads. They only appeared as a coherent package
about 50,000 years ago, and the first modern humans to emerge from the
area of the Middle East nearest to Africa between 50,000 and 40,000
years ago seem to have had the full set.
As modern human anatomy is documented at earlier
and earlier sites, it becomes evident that there was a great time
gap between the appearance of the modern skeleton and 'modern
The study moved the date of human skulls found in
Ethiopia's Kibish rock formation in 1967 back from 130,000 years to a
newly determined date of 195,000 years ago, give or take five thousand
years. Fossils from an individual known as Omo I look like bones of
modern humans, but other bones are from a more primitive cousin named
In addition to the cultural question, the earlier date for
humanity's emergence is important for other reasons.
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Early Cultures of the Middle East
College of Mines and Earth Sciences
University of Utah
Ethiopia's River Omo flows below
bluffs of the Kibish rock formation, where scientists
first excavated the bones of early humans in 1967 and
estimated that they were 130,000 years old. But in a 2005
study, scientists determined that those bones and newly
excavated fossils actually were from humans who roamed the
area 195,000 years ago.
The study was funded by
the National Science Foundation, the LSB Leakey Foundation,
the National Geographic Society, and the Australian National
Firstly, it makes the dates in the fossil record
almost exactly concordant with the dates suggested by genetic studies
for the origin of modern man. Secondly, it placed the first appearance
of modern Homo sapiens in Africa many more thousands of years
before our species appears on any other continent. It lengthens that
gap. Finally, the similar dating of the two skulls indicated that when
modern humans first appeared there were other contemporary populations
- such as Omo II - that were less modern.
Modern Homo in the valley of the Omo
In 1967 Richard Leakey and his team of palaeontologists
travelled to the Kibish Formation along the River Omo in southernmost
Ethiopia, near the town of Kibish. They found the skull (minus the
face) and partial skeleton (parts of arms, legs, feet, and the
pelvis) of Omo I, and the top and back of the skull of Omo II.
Brown was not part of the 1967 expedition, but was
working nearby and got to look at the site and the fossils.
Anthropologists at the time were noting how very different they
looked in their evolutionary status. Omo I essentially appeared
to be modern Homo sapiens, and Omo II appeared to be more
In 1967, the fossils were dated at 130,000 years
old, although the scientists doubted the accuracy of their dating
technique, which was based on the decay of Uranium 238 to
Thorium 238 in oyster shells from a rock layer near the skulls.
No scientist has been bold enough to suggest that Omo
II is anything other than Homo sapiens. Instead, it is quite
often the case that, at the time of major events in evolution, one
finds an increase in morphological - anatomical - diversity.
With the 2005 study confirming Omo I and Omo II as
being the same age, living within a few hundred years of each other
at about 195,000 years ago, some anthropologists suggested that Omo
II perhaps was not so primitive after all.
McDougall, Brown, and Fleagle and researchers from
other universities returned to Kibish in 1999, 2001, 2002, and 2003.
They identified sites at which Omo I and Omo II were found in 1967,
and obtained more of Omo I, including part of the femur (upper leg
bone) that fitted to a piece found in 1967. They also found animal
fossils and stone tools, and studied local geology. The 2005 study
included initial results from those expeditions.
The fossil record of human ancestors may go back
six million years or more, and the genus Homo arose at least
1.8 million years ago when australopithecines evolved into potential
direct-line human ancestors known as Homo habilis (see the
Hominid Chronology for details). The fossil record for humans
is poor between 100,000 to 500,000 years ago, so Omo I is significant
because it is well dated.
Dating the dawn of humanity
Both Omo I and Omo II were buried in the lowermost
portion or 'member' of the Kibish Formation, a series of annual flood
sediments laid down rapidly by the ancient River Omo on the delta
around where it once entered Lake Turkana. Lake levels now are much
lower, and the river enters the lake about a hundred kilometres
(sixty miles) south of Kibish.
The formation is a hundred metres thick (330 feet),
and is divided into at least four members, with each of the four
sets of layers separated from the other by an 'unconformity', which
represents a period of time during which rock eroded away instead
of being deposited.
For example, the lowermost Kibish I member was
deposited in layers as the River Omo flooded each year. After
thousands of years, rainfall diminished, lake levels dropped, and
the upper part of Kibish I eroded away. Later, the lake rose and
deposition resumed to create layers of Kibish member II.
Interspersed among the river sediments are
occasional layers of volcanic ash from ancient eruptions of
nearby volcanoes. Some ash layers contain chunks of pumice,
which in turn contain feldspar mineral crystals. Feldspar has
small amounts of radioactive Potassium 40, which decays into
Argon 40 gas at a known rate. The gas, trapped inside feldspar
crystals, allows scientists to date the feldspar and the pumice
and ash encasing it.
A reconstruction of Omo I, one of the very earliest examples of
anatomically modern humans ever to appear in the archaeological
record at 195,000 years ago
Potassium-argon dating shows that a layer of ash no more than three metres
(ten feet) below Omo I's and Omo II's burial place is 196,000 years old,
give or take two thousand years. Another layer is 104,000 years old. This
one is almost fifty metres (160 feet) above the layer that yielded the Omo
humans. The unconformities represent periods of time in which rock was
eroded, so that the fossils must be much older than the 104,000 year-old
layer and close in age to the 196,000 year-old layer.
The clinching evidence comes from sapropels, which are
dark rock layers on the Mediterranean sea floor that were deposited
when floods of fresh water poured out of the River Nile during rainy
The Blue Nile and White Nile tributaries share a
drainage divide with the River Omo. During ancient wet periods,
monsoons on the Ethiopian highlands sent annual floods surging down
the Nile system, causing sapropels to form on the sea floor, and sent
floods down the Omo, making Lake Turkana rise and depositing Kibish
Formation sediments on the river's ancient delta. (During dry
periods, Lake Turkana was smaller, flood sediments were deposited
farther south and rocks at Kibish were eroded.)
No other sediments on land have been found to record
wet and dry periods that correlate so well with the same climate pattern
in ocean sediments. The 2005 study found that the 'members', or groups,
of rock layers in the Kibish formation were laid down at the same time
as the Mediterranean sapropels. In particular, the volcanic layer right
beneath Omo I and II dates to 196,000 years ago by potassium-argon dating,
and corresponds almost perfectly to a sapropel layer previously dated as
195,000 years old.
The study team members decided that it was pretty
conclusive, disputing any contention that the fossils might be
younger than 195,000 years old.
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