Oh, I'm so thirsty...those Neandertals sure have a lot of water...
Here's the main idea of this BBC story:
Scientists are increasingly convinced that tragedies in the deep past have shaped human evolution.
Well, that is certainly true. "Scientists" are increasingly convinced.
The story is about an ancient drought in Africa:
Scientists have identified a major climate crisis that struck Africa about 70,000 years ago and which may have changed the course of human history.
The evidence comes from sediments drilled up from the beds of Lake Malawi and Tanganyika in East Africa, and from Lake Bosumtwi in Ghana.
It shows equatorial Africa experienced a prolonged period of drought.
It is possible, scientists say, this was the reason some of the first humans left Africa to populate the globe.
The thing about these major environmental events in the past is that they clearly happened; their dramatic nature is why we know about them at all. And it seems churlish to point out that we actually have no evidence of a link between these massive environmental insults and human populations.
But it just doesn't make much sense.
The hypothesis is that a major drought in southeastern Africa effectively ejected some human populations from the continent into Eurasia, where they succeeded beyond anyone's wildest expectations. It's like the baby bird in a nest: all we needed was a little push, and we could fly!
Expressed that way, it isn't too hard to see the flaw: if humans could succeed in Eurasia after a drought forced them out of Africa, then they certainly could have succeeded there without any drought at all. The idea that they were "too comfortable" in their African homeland to move is just nonsensical -- if they were a successful population, then intrinsic population growth would force them to expand sooner or later anyway. If they were blocked from leaving Africa by ecological limits, then no drought would make them suddenly able to transcend those limits.
In other words, the drought is completely unnecessary to explain anything.
Notice how we never hear about the environmental catastrophes that didn't supposedly spur some kind of human migration. Like the last Yellowstone eruption. Now that would make a story.
Recent megatsunamis
The NY Times has an article by Sandra Blakeslee describing geological evidence for recent (i.e. Holocene) megatsunamis:
The explanation is obvious to some scientists. A large asteroid or comet, the kind that could kill a quarter of the world's population, smashed into the Indian Ocean 4,800 years ago, producing a tsunami at least 600 feet high, about 13 times as big as the one that inundated Indonesia nearly two years ago. The wave carried the huge deposits of sediment to land.
It's set up as an opposition between these geologists (notably, Dallas Abbott) and astronomers, who don't think there are enough big space rocks to cause that many recent impacts.
And of course there is the requisite mythical flood connection:
Dr. Masse analyzed 175 flood myths from around the world, and tried to relate them to known and accurately dated natural events like solar eclipses and volcanic eruptions. Among other evidence, he said, 14 flood myths specifically mention a full solar eclipse, which could have been the one that occurred in May 2807 B.C.
(via Gene Expression)
Bioturbation in the Cambrian
John Wilkins has a neat post about the effects of the first burrowing worms during the Cambrian, based on a recent paper. It starts with this irresistible line:
Quick... what was Darwin's most popular book? If you answered The Origin of Species, you were wrong.
You'll have to click for the answer. It's a neat post if you're interested in bioturbation from a different point of view than archaeology.
The Great Rift Valley
The climate of the Early Pliocene differed from that of the Miocene primarily by the appearance of a cooling and drying trend across Africa, where early hominids evolved. It is likely that these climatic changes led to a decrease in the forest cover of large parts of the African continent.
Some of the climatic conditions of the early Pliocene were indirect effects of tectonic activity on the African continent. The most important manifestation of Africa's geology, beginning some twenty million years ago, is the formation of the Great Rift Valley. The Great Rift is an ocean being born, as parts of East Africa pull away from the rest of the continent, leaving a sinking basin in their wake. This geology is not limited to Africa, but stretches into West Asia, causing the Dead Sea to occupy the lowest continental basin on Earth, and continuing to generate earthquake activity as far north as Anatolia.
The first stages of geologic changes in East Africa involved massive uplift, resulting in vast highlands stretching from Ethiopia in the north to Mozambique in the south. The origins of these highlands apparently led to a disruption in the normal atmospheric circulation across Africa, creating a rain shadow on the easternmost edge of the continent, and fragmenting the rain forest that stretched across the equatorial region of Africa during the early Miocene. Later, geologic rifting lowered the center of the vast highland region, creating a second rain shadow and yet more biotic fragmentation. This process of habitat fragmentation has been suggested to be at the root of the evolutionary changes witnessed in late Miocene apes and early hominids. As expressed by French paleoanthropologist Yves Coppens, this hypothesis has been called the "East Side Story," as it placed the origin of the first hominids to the east of the rift, contrasting with other African apes to the west (Coppens, 1984).
The history of uplift and rifting also created a unique environment for the preservation and recovery of ancient fossil remains. Over time, the rifting created new river systems and a series of great lakes along the eastern edge of the continent, including present-day Lake Victoria, Lake Malawi, Lake Tanganyika, and Lake Turkana. These lakes have had complex histories as ancient faults moved and shifted their shores and the rivers that fed them. These movements have left the sediments of ancient lakes and rivers exposed, and the precious fossils that they bear today erode from these sedimentary rock layers. The fossils bear clues about paleoenvironments as well as about the ancient species that they represent, and it is from these clues that we can reconstruct the habitats and adaptations of early hominids.
Although early hominids were highly preserved in the East African rift context, they may not have actually originated there. Recently, discoveries to the west of the rift, including those at Bahr el Ghazal and Toros-Menalla in Chad, have pointed to the possibility that hominids existed in Central and West Africa as well. It may be that the formation of the rift and the consequent changes in East African climate actually had little or nothing to do with hominid origins. In this case, the "East Side Story" would be wrong.
A side effect of the tectonic rifting is volcanism, which has left its own distinct mark on the paleoanthropological record. The largest mountains in East Africa are volcanoes, including Mounts Kenya and Kilimanjaro, the Virungas, and the vast Ngorongoro crater. These mountains and other ancient volcanoes periodically erupted during the Pliocene and Pleistocene, spreading layers of volcanic ash and pumice across broad areas. As these ashfalls accumulated over time, they formed rock layers called tephra, which are interleaved with other sedimentary layers in the East African geology. Because of their volcanic origin, these tephra can be absolutely dated using radiometric methods, providing a nearly unparalleled sequence of sediments in time, a sequence that can be correlated among sites and can provide very precise dates for important fossil specimens (Feibel, 2001).
The Kansas meteorite excavation
This is a neat story:
GREENSBURG, Kan. - Scientists located a rare meteorite in a Kansas wheat field thanks to new ground penetrating radar technology that some day might be used on Mars.
The dig Monday was likely the most documented excavation yet of a meteorite find, with researchers painstakingly using brushes and hand tools in order to preserve evidence of the impact trail and to date the event of the meteorite strike. Soil samples were also bagged and tagged, and organic material preserved for dating purposes.
Even before they had the meteorite out of the ground, the scientific experts at the site were able to debunk prevailing wisdom that the spectacular Brenham meteorite fall occurred 20,000 years ago. Its location in the Pleistocene epoch soil layer puts that date closer to 10,000 years ago.
The "Brenham" meteorite was a 450 kg specimen found in 1949, and pieces of the same impactor are all over the county. An even bigger chunk was found last year only a mile or two away, and it was the third biggest of its type ever found. This is another piece of the same rock, but found in the ground so that they can date it.
I find it interesting that here we have a highly dispersed resource, which probably occurs with nearly equal probability anywhere in the world, but very rarely. So a few people have specialized to find them, because they are scientifically interesting and worth a lot of money. And they used to be limited to looking in places with lots of permanent ice (where melts made them easy to find on the surface) or places with very little vegetation, like deserts, where -- again -- they are stuck on the surface.
But technology has made it possible to find them in a broader range of contexts, so it's an open field for searching. Of course, in this case there's a reason to look harder, since there are fragments of the same ancient meteorite all over the county.
A little night music
Mars and the moon are in conjunction tonight, as I happened to notice outside. With a full moon they are a spectacular show.
Sometimes it takes actually seeing celestial bodies sidling up to each other to remember that they are out there, pulling on the sun like buckets on the end of a rope. Except the moon -- it is pulling on us, sluicing the tides around the world. Now Mars is near opposition, and from here it will slide a bit farther west every night until it reaches the sunset. And all this because we are overtaking it, because we are swinging faster in our orbit around the sun.
I have a clear mental image of the full moon -- usually the full moon rising over the eastern horizon or low in the southeastern sky. In that position it seems the biggest, and you read all the time about why the illusion of a larger moon seems so real.
But it takes seeing the moon next to a planet, way overhead, to realize there's something wrong with the image. When you see the rising moon, you're looking at it sideways, with the north pole on the left. When you look at the moon right overhead, with your head in the north, it looks a bit unfamiliar, a bit strange. That's the way it's spinning, once every time it revolves around us.
And every time it goes around us, it goes a tiny bit slower, like a spinning figure skater letting her arms out. Because that's exactly what's happening; it's getting a bit farther away.
Mars is a bit further from us at this opposition than the last one, 26 months ago. Then, it was very near perihelion, and close to the sun means close to us as well. In fact, it was closer in 2003 then at any time in the last 59,000 years. NASA even commissioned an artist's conception of a Neandertal family watching it.
Of course, you know the Neandertals are stupid because they are looking away from the red orb in the sky.
Psst...wanna buy a mammoth?
A local story:
MILWAUKEE - A 76-year-old Kenosha County man in whose cornfield the skeleton of a mammoth believed to be about 12,500 years old was dug up in 1994 is interested in selling it, and officials of the Milwaukee Public Museum are interested in it.
He's got the mammoth in wooden crates in his basement.
Experts have suggested the bones could be worth from between $100,000 to $500,000.
...
Hebior [the owner] said an effort to sell the bones several years ago failed because the bids that came in were too low.
A number of Siberian mammoth skeletons sold after the fall of the Soviet Union might have suppressed the market, said Dan Joyce, senior curator of the Kenosha Public Museum.
That gives a whole new meaning to "bioprospecting!"
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks