28 November 2010

Ancient Lakes and Siberian Mammoths

An Ancient Lake in the Sahara

[A] lake [now called Lake Tushka] broader than Lake Erie once sprawled a few hundred kilometers west of the Nile, researchers report in the December issue of Geology. Since the lake first appeared around 250,000 years ago, it would have ballooned and shrunk until finally petering out around 80,000 years ago. Knowing where and when such oases existed could help archaeologists understand the environment Homo sapiens traveled while migrating out of Africa for the first time[.]

From here.

Lake Tushka would have filled an area parallel to the Nile in Egypt to the Sudanese border and would have been filed by Nile flooding. Adjacent areas at the time would have been grassland.

There is a tendency to rule out North Africa as a place where the earliest modern humans could have lived around the time of the Out of Africa migration, but it would have been far more liveable at that time.

A Late Demise For Siberian Megafauna

Sergey Zimov and his son Nikita argue that overkill by humans for "food, fuel or fun" rather than climate shift per se, drove "shaggy mammoths, woolly rhinos and bison" in Northern Siberia to extinction "about 10,000 years ago — in the span of a geological heartbeat, or a few hundred years." While scientists dispute whether their demise was due to overkill, climate shift, or both, however, the timing of the megafauna extinction in Northern Siberia is not seriously disputed except to a small degree at the margins.

What makes this remarkable?

Hominins have been in Asia for hundreds of thousands of years, in Homo Erectus form, and modern humans were present in Northern Siberia and Tibet for tens of thousands of years before the Last Glacial Maximum of 20,000 years ago, retreated to the Southern margin of that territory as the ice age reached its peak, and then returned as the glaciers receded. Yet, the extinction of megafauna in Northern Siberia is roughly contemporaneous with the comparable megafauna extinction in the Clovis period in North America where modern humans had just arrived on the scene.

In contrast, there were major megafauna extinctions in Europe and Australia much earlier after the arrival of modern humans. The mystery then, is not why humans were probably an important factor in killing off the megafauna of Northern Siberia, but why it didn't happen much sooner.

Ten thousand years ago agriculture was just starting to arise in the Near East, but had not yet reached Pakistan or Egypt, where it spread next, let alone Europe, and had also not arisen yet in either North China or South China, the closest points where agriculture arose.

The only domesticated animal at the time of the Northern Siberian megafauna extinctions was the dog. The mammoth hunters of Northern Siberia lacked horses, donkeys, and camels, for example.

If climate mattered, it may have done so by allowing more hunters onto the Steppe, rather than by impairing the ability of its ice age large animals to survive.

1 comment:

Maju said...

Thanks for two nice pieces.

I've always thought that the Nile basin may have been an important early human area, what does not matter for pointing rather towards Ethiopia or the Sudan-Ethiopia joint area as more likely core of early humankind (they are also in the Nile basin, as are Uganda, Kenya and even further south). The main reason for looking specially at the Sudan/Ethiopia area is genetic, rather than archaeological, as there are modern humans in North Africa that are similarly old as those from Ethiopia (c. 190 Ka ago).

As for the mammoths, you say: "If climate mattered, it may have done so by allowing more hunters onto the Steppe, rather than by impairing the ability of its ice age large animals to survive".

Actually it mattered in the sense that warm climate always restricted a lot the areas where mammoths could thrive. However they could still survive in previous interglacial periods, so the human impact should not be underestimated either.