Skip to comments.Late Pleostocene Human Population Bottlenecks. . . (Toba)
Posted on 12/16/2005 11:33:44 AM PST by blam
Professor Stanley H. Ambrose Department of Anthropology, University Of Illinois, Urbana, USA
Extract from "Journey of Human Evolution"  34, 623-651
The last glacial period was preceded by 1000 years of the coldest temperatures of the Late Pleistocene, apparently caused by the eruption of the Mount Toba volcano. The six year long volcanic winter and 1000-year-long instant Ice Age that followed Mount Toba's eruption may have decimated Modern Man's entire population. Genetic evidence suggests that Human population size fell to about 10,000 adults between 50 and 100 thousand years ago. The survivors from this global catastrophy would have found refuge in isolated tropical pockets, mainly in Equatorial Africa. Populations living in Europe and northern China would have been completely eliminated by the reduction of the summer temperatures by as much as 12 degrees centigrade.
Volcanic winter and instant Ice Age may help resolve the central but unstated paradox of the recent African origin of Humankind: if we are all so recently "Out of Africa", why do we not all look more African?
Because the volcanic winter and instant Ice Age would have reduced populations levels low enough for founder effects, genetic drift and local adaptations to produce rapid changes in the surviving populations, causing the peoples of the world to look so different today. In other words, Toba may have caused Modern Races to differentiate abruptly only 70,000 years ago, rather than gradually over one million years.
The Mount Toba eruption is dated to approximately 71,000 years ago. Volcanic ash from Mount Toba can be traced north-west across India, where a widespread terrestrial marker bed exists of primary and reworked airfall ash, in beds that are commonly 1 to 3, and occasionally 6 meters [18 feet] thick.
Tambora, the largest known historic eruption, displaced 20 cubic kilometres of ash. Mount Toba produced 800 cubic kilometres.* It was therefore forty times larger than the largest eruption of the last two centuries and apparently the second largest known explosive eruption over the last 450 million years.
*Mount St Helens produced a tiny 0.2 cubic kilometres.
Volcanic Winter, and Differentiation of Modern Humans
Mount Toba's eruption is marked by a 6 year period during which the largest amount of volcanic sulphur was deposited in the past 110,000 years. This dramatic event was followed by 1000 years of the lowest ice core oxygen isotope ratios of the last glacial period. In other words, for 1000 years immediately following the eruption, the earth witnessed temperatures colder than during the Last Glacial Maximum at 18-21,000 years ago.
For the volcanic aerosols to be effectively distributed around the earth, the plume from the volcanic eruptions must reach the stratosphere, a height greater than 17 kilometres. Mount Toba's plume probably reached twice this height. Most solar energy falls at low latitudes between the Tropics of Cancer and Capricorn, so eruptions that happen near the Equator cause much more substantial cooling due to the reflection of solar energy. Toba lies 2 degrees north of the Equator, on the Island Sumatra.
The reduction in atmospheric visibility due to volcanic ash and dust particles is relatively short-lived, about three to six months. Longer-term global climatic cooling is caused by the highly reflective sulphuric acid haze, which stays suspended in the upper atmosphere for several years.
Ice core evidence implicates Mount Toba as the cause of coldest millennium of the late Pleistocene. It shows that this eruption injected more sulphur that remained in the atmosphere fo a longer time [six years] than any other volcanic eruption in the last 110,000 years. This may have caused nearly complete deforestation of southeast Asia, and at the same time to have lowered sea surface temperatures by 3 to 3.5 degrees centigrade for several years.
If Tambora caused the " The year without a summer" in 1816, Mount Toba could have been responsible for six years of relentless volcanic winter, thus causing a massive deforestation, a disastrous famine for all living creatures, and a near extinction of Humankind.
The Volcanic Winter/Weak Garden of Eden model proposed in this paper. Population subdivision due to dispersal within African and other continents during the early Late Pleistocene is followed by bottlenecks caused by volcanic winter, resulting from the eruption of Toba, 71 ka. The bottleneck may have lasted either 1000 years, during the hyper-cold stadial period between Dansgaard-Oeschlger events 19 and 20, or 10ka, during oxygen isotope stage 4. Population bottlenecks and releases are both sychronous. More individuals survived in Africa because tropical refugia were largest there, resulting in greater genetic diversity in Africa.
Bahamas Coral Reef Chart
BLOMBOS CAVE : 77,0000 YEARS OLD
Small and portable, this red ochre stone is engraved with what must be "tally" marks. It is one of two such stones recently found in the Blombos Cave in South Africa and have been dated as being 77,000 years old, making them the oldest form of recorded counting ever found.
The stone is worn which probably indicated that it was constantly handled over a period of time, how long is impossible to tell. It looks as though the stone has been reused at least once before as the lighter marks appear to have been erased rather than worn away naturally.
If the dating is accurate this stone was used 5000 years before the Mount Toba eruption of 71,000 years ago. The evidence from the Toba eruption indicates that the world's population of Modern Man was reduced to a total of around 10,000 adults.
I expect that we'll eventually find that humans were stranded in South America during the Volcano Winter caused by the Toba explosion and were not re-united with the world's other humans until thousands of years later.
I grabbed Kwares Erupt program.
Tried to simulate Toba.
To get the amount of volcanic gunk to erupt that Toba did, you have to simulate an eruption lasting over one year.
Toba erupted its load in less than that.
I have heard speculation that during the last third or so of the last great ice age, worldwide population fell to the 10-20K range.
I guess we're talking about 12-15 K years ago.
Last I checked, ice was water.
I seem to recall Toba was a Caldera.. like the one sitting under Yellowstone... does Kwares Erupt even have the capacity to simulate a Caldera eruption?
I think you're thinking of the Last Glacial Maximum(LGM), 18-23,000 years ago. That was an extremely cold period and this Journey Of Mankind shows an extreme shrinkage of humans worldwide during that period. I've not seen any population figures associated with that period though.
Yes. Super Volcano status.
I've seen some discussion on up-grading the Thera eruption some...not to super volcano status though.
The above looks like a moderne style menorah. Very nice design.
Placemark, I look forward to reading this.
i have a question for you...how does the author know that those lines on the rock are tally marks and not just the grooves left when someone sharpened a stick or arrow head on that rock?
Stones used for sharpening tend to have more, and deeper scratches, and they are generally more central. Sometimes they have a single deep "V"-shaped groove.
This stone matches the world-wide pattern you find with non-sharpening (i.e., ceremonial, counting, etc.) stones.
Check out a book title "Patterns that Connect: Social Symbolism in Ancient & Tribal Art" by Schuster and Carpenter for illustrations.
Proud member of Haplogroup G2 :^)
Yes, but only up to a point.
Whew! I was hoping you'd step forward and answer that one, lol.
ping for great discussion topic
Looking back into the program, it simulates only two types of caldera, Valles type, and Mazama type.
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