A beautiful hellscape

One of the strangest places on Earth is in eastern Ethiopia.  Not that many people have even heard of it, for the very good reason that if you go there, there are about a million and one ways you could die.

It's called Dallol, which comes from a word in the Afar language meaning "disintegration."  The name comes from the fact that this is what would happen to you if you went for a swim there.  It lies in the Danakil Depression, and is a maze of hot springs, filled with water that gets up to 95 C and can have a pH of less than 1.  It's surrounded by evaporite plains covered with layers of magnesium, calcium, and iron oxide, crystalline salt, and elemental sulfur.

The place doesn't even look real:

[Image licensed under the Creative Commons Kotopoulou Electra, The hydrothermal system of Dallol, CC BY-SA 4.0]

The highest elevation in Dallol is 48 meters below sea level.  The region gets ridiculously hot -- think Death Valley in midsummer -- so tourism, even if you were so inclined, is pretty much out of the question.

Where it gets even more interesting is why, if the place is entirely below sea level, it's not under water.  And this has to do with the geology of the region, and how it was created in the first place.

Dallol and the Danakil Depression are part of the East African Rift System, which formed in the Miocene Epoch on the order of fourteen million years ago.  Basaltic magma upwelling from the mantle created a crack in the Earth's crust and began to fracture the African Plate.  This generated a long rift valley running more-or-less northeast to southwest, from the shore of the Red Sea in Ethiopia, under Lake Victoria, then southward through Tanzania and all the way to Malawi.  The entire thing is seismically active, but the north end especially so, experiencing nearly constant earthquakes and volcanic eruptions -- not to mention a huge amount of hydrothermal activity, such as you see at Dallol.

The water of the Red Sea is currently being held back by the barrier of the Erta Ale Range, which blocks the East African Rift Valley on its northeastern end.  Eventually, though, the barrier will be breached as the rift continues to open up, and the water will come pouring in.  At that point, all of Dallol and the Danakil Depression -- and a large part of the rest of the valley -- will be an inlet of the Indian Ocean.

That won't stop the rift from continuing to spread, though.  The entire "Horn of Africa" will separate from the rest of the continent and go sliding off to the east.  As I've pointed out before, it's only our short life spans that make us think the current configuration of continents is permanent.

For now, though, the Erta Ale Range is holding the ocean back, allowing us to take a look at one of the most inhospitable places on Earth.  What I find most curious is that a part of this same system of rifts -- farther south, in Kenya and Tanzania -- is thought to be the cradle of humanity.  Much of the history of our earliest ancestors, species like Paranthropus and Australopithecus and Ardipithecus, took place here.  Somehow they dealt with the heat and drought and seismic activity (as well as the predators), surviving long enough to evolve into Homo sapiens, who then pretty much rushed out and took over the whole planet.

Odd to think that a beautiful hellscape was where humanity first got its start.

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Out of Africa

In a rather startling coincidence, just yesterday I wrote about how much the course of human evolution was constrained by our evolving in a place that had large predators, scarce resources, and seasonal drought, and almost simultaneously a paper was published in Nature Geoscience about exactly that.

A huge interdisciplinary team of geoscientists, sedimentologists, micro-paleontologists, geologists, geographers, geochemists, archaeologists, chronologists, evolutionary biologists, and climate modelers led by Verena Foerster of the University of Cologne set themselves a mammoth task -- to correlate shifts in climate in East Africa over the past 620,000 years with patterns of population growth, evolution, and dispersal amongst the hominin species that lived there. 

Starting with two 280-meter-long continuous sediment cores from the Chew Bahir Basin in southern Ethiopia, the team was able to analyze not only the sediment geology and chemistry, but such things as pollen and seed types, fossil content, and rate of deposition to infer what the climate was doing at the time.  What they found was that from 620,000 to 275,000 years ago, the climate was amazingly stable -- warm and humid -- but that interspersed through that time were short, abrupt, extreme drought phases.  These "arid pulses" led to sudden habitat fragmentation, as the climatic shifts didn't hit everywhere at once (nor with equal severity).  Some areas remained relatively wetter, while other areas not that far away were experiencing catastrophic drought.

When this happens -- a large swath of relatively uniform habitat becomes unstable and/or patchy -- it generally has two results; (1) animals become more mobile, migrating in search of resources that are now less reliable; (2) organisms less capable of moving undergo strong selective pressure to adapt to "the new normal."  Both of these affected our ancient relatives.  Some began to disperse more widely, presumably seeking out food and water, while others diversified in response to their new local climatic conditions, leading to rapid speciation.

Following this, the East African climate began to undergo more regular oscillations between congenial and hostile.  Wet phases, with abundant vegetation and deep freshwater lakes, alternated with dry phases during which the lakes evaporated almost completely, leaving only highly saline, alkaline ponds.  During this time, the Acheulean hand axe culture of the Lower Paleolithic (associated with our predecessor species Homo ergaster) was superseded by more sophisticated technologies and the emergence of modern Homo sapiens about sixty thousand years ago.

An Acheulean hand axe [Image licensed under the Creative Commons José-Manuel Benito Álvarez (España) —> Locutus Borg, Bifaz cordiforme, CC BY-SA 2.5]

Things only got dicier from there.  Between sixty and ten thousand years ago -- the highest layers of the sediment cores -- East Africa saw the most arid phase in the entire record.  This had two effects -- driving our ancestors out of Africa in search of better conditions, and triggering the extinction of virtually all our near relatives.  We won, apparently, by dint of our mobility and large brains, allowing us to cope with hostile and rapidly fluctuating conditions, eventually leading to our dispersing to every habitable land on Earth.

It's fascinating to me that we owe our own existence to fluctuations in the climate -- that the conditions in one part of the world molded us into the species we currently are.  Now that we have technology to avoid many of the caprices of the environment, we are also shielded from their evolutionary effects; you have to wonder how (or if) our distant descendants will be altered by climate shifts, more specifically those we ourselves are perpetrating.  It once again brings home the truth of the perspective that each species is not a separate entity, but is part of an intricate tapestry of life.  Pull on one thread, and the others will inevitably, and irrevocably change -- for good or ill.

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A new twig on the family tree

My long-ago professor of evolutionary biology, Dr. Andrew Collins, once said, "The only reason humans came up with the concept of species as little air-tight boxes is that we have no near relatives still alive."  After a pause, he added, "And it's also the reason why evolution isn't completely self-evident to everyone."

I've always remembered that -- the word "species" is an artificial construct, and is the hardest concept in biology to come up with a consistent definition for.  No matter how you define it, you come up with exceptions and qualifications (something I dealt with a while back in my post "Grass, gulls, mosquitoes, and mice"), and it's only our determination that nature should be pigeonholeable (to coin a word) that keeps it in the textbooks.

We had a lovely example of that announced this week, when we learned that a stunningly well-preserved 3.8-million-year-old skull from Ethiopia had been identified as Australopithecus anamensis.  This species had been thought ancestral to A. afarensis (the species to which the famous Lucy belonged), but the Ethiopian skull (nicknamed MRD after Miro Dora, the site where it was discovered) is the same age as the earliest clearly A. afarensis remains.

So it looks like the two coexisted at least for a while, which is actually a much more common thing than the textbook one-species-slowly-morphing-into-another model.  Take, for example, our own (much more recent) ancestry, when only fifty thousand years ago there was enough interbreeding between Neanderthals, Denisovans, and anatomically-modern humans that we still find significant traces of each of those lineages in our own DNA.  (When I had my own DNA sequenced, I was proud to find out that I had 284 clearly Neanderthal markers, putting me in the 60th percentile and possibly explaining why I eat my t-bone steaks rare and like running around with little to no clothing on.)

The current discovery, though, is awfully cool.  Here's the skull itself, and a reconstruction of what its owner might have looked like, by the amazing John Gurche:

[Images courtesy of Jennifer Taylor, Dale Mori, and Liz Russell (right); and John Gurche and Matt Crow (left)] 

As an aside, John Gurche lives in the same little upstate New York village that I do, and I was privileged to teach all three of his kids.  His son, Loren, is now a paleontologist in his own right, and even when he was an eleventh grader in my AP Biology class he so clearly knew more about extinct animals than I did that I gladly asked him to contribute every time the topic came up in class.

Anyhow, the whole thing is wicked cool.  Picture it; an African savanna with not just one, but several different kinds of proto-hominins running around, some of them quite human-like and others more similar to our ape ancestors.  I'm always a little astonished at people who find the idea of our non-human ancestry demeaning -- I think it's grand that we're connected, in a series of unbroken links extending back three billion years, to every other life form on Earth.

And the whole thing took place, for the most part, in a smooth set of small changes, almost indistinguishable without the advantage of a huge time scale.  As Charles Darwin put it in The Descent of Man, "In a series of forms graduating insensibly from some apelike creature to man as he now exists, it would be impossible to fix on any definite point where the term 'man' ought to be used."

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This week's Skeptophilia book recommendation is about a subject near and dear to my heart; the possibility of intelligent extraterrestrial life.  In The Three-Body Problem, Chinese science fiction writer Cixin Liu takes an interesting angle on this question; if intelligent life were discovered in the universe -- maybe if it even gave us a visit -- how would humans react?

Liu examines the impact of finding we're not alone in the cosmos from political, social, and religious perspectives, and doesn't engage in any pollyanna-ish assumptions that we'll all be hunky-dory and ascend to the next plane of existence.  What he does think might happen, though, makes for fascinating reading, and leaves you pondering our place in the universe for days after you turn over the last page.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]