We're Still Standing

A study of ancient volcanic ash found at key archaeological sites across Europe suggests that early modern humans were more resilient to climate change and natural disasters than commonly thought. The study, which appeared in PNAS, analyzed volcanic ash from a major eruption that occurred in Europe around 40,000 years ago. The volcano spewed so much ash that the event probably created winter-like conditions and a sudden colder shift in climate. Scientists have generally suggested that the spread of modern humans, and the decline of our cousins the Neanderthals, was primarily due to ancient volcanic eruptions and deteriorating climate conditions, but this study shows that stone-age man rolled with the punches and shrugged off the sudden shifts in climate. This new evidence flies in the face of modern predictions that a shift of a few degrees in average yearly temperature will decimate human populations world wide.

The Response of Humans to Abrupt Environmental Transitions (RESET) project is a research initiative launched in 2008 and funded by the Natural Environment Research Council (UK). It brings together archaeologists, vulcanologist, geochemists, oceanographers and paleontologists to investigate the chronology of major phases of human dispersal and development in Europe and North Africa during the past 100,000 years and examine the degree to which these phases were influenced by abrupt environmental transitions (AETs). RESET funded the paper, “Volcanic ash layers illuminate the resilience of Neanderthals and early modern humans to natural hazards,” by John Lowe et al. that appeared in the July 23 issue of PNAS. Here is a summary of the authors' motivation and findings:

Marked changes in human dispersal and development during the Middle to Upper Paleolithic transition have been attributed to massive volcanic eruption and/or severe climatic deterioration. We test this concept using records of volcanic ash layers of the Campanian Ignimbrite eruption dated to ca. 40,000 y ago (40 ka B.P.). The distribution of the Campanian Ignimbrite has been enhanced by the discovery of cryptotephra deposits (volcanic ash layers that are not visible to the naked eye) in archaeological cave sequences. They enable us to synchronize archaeological and paleoclimatic records through the period of transition from Neanderthal to the earliest anatomically modern human populations in Europe. Our results confirm that the combined effects of a major volcanic eruption and severe climatic cooling failed to have lasting impacts on Neanderthals or early modern humans in Europe. We infer that modern humans proved a greater competitive threat to indigenous populations than natural disasters.

Note that the Campanian Ignimbrite eruption was no minor volcanic event. It left behind a large, 13 kilometer (8.1 mile) wide caldera situated to the west of Naples, Italy. No less than 150 km3 of magma were extruded in the CI eruption, the ash from which can be detected in Greenland ice cores. Today, lying mostly underwater, the area comprises 24 craters and volcanic edifices. Many anthropologists have credited climate change engendered by the CI eruption with killing off the Neanderthals. But that is not what Lowe et al. found.


Location of the Campanian Ignimbrite eruption.

The Neanderthals disappeared about 30,000 years ago, but what caused their demise is still a subject of fierce debate. Some argue that it was us—Homo sapiens, ie. modern humans—who drove the Neanderthals to extinction. One camp suggests that invading waves of early modern humans genetically absorbed them, others put forth less gentle mechanisms for the Neanderthals' removal. Explanations range widely, encompassing disease, warfare, economic competition from early modern humans, or the impact of climate change.

According to the researchers, the RESET Project set out to establish whether cryptotephra layers could be traced to important archaeological and geologic sites in Europe, the fringe of North Africa and the Middle East, and the Mediterranean Sea, with a key objective being to synchronize records that span the Middle Paleolithic (MP) to Upper Paleolithic (UP) transition. To accomplish this, the researchers had to examine microscopically thin layers of sediment from all over Europe and under the seas. An example of what they were looking for is shown below. Each shard is less than 125 microns in size.


Optical microscope image of vesicular tephra and volcanic shards.

The key hypothesis to be tested by RESET funded research is whether the archaeological visibility of Homo neanderthalis and Homo sapiens populations is determined by AETs: declining during cold phases and increasing during interstadials. To try and answer these questions, researchers are examining hundreds of sites, some of which are listed in the figure below. MIS stands for marine isotope stage, alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data.


Chronological chart of key research sites.

Lowe et al. found identifiable volcanic ash from a large eruption at several archaeological sites in Europe and North Africa. Using these findings, they were able to link events in Neanderthal and human evolution with the timing of climatic changes. Their work indicates that early modern humans started to displace Neanderthals from parts of Europe before the eruption and the cooling that followed. In parts of central and eastern Europe, Neanderthals became extinct well before the eruption occurred. Moreover the activities of both species appear to have been unaffected by the CI event and its aftermath. The authors' conclude that climate change didn't kill off the Neanderthals or greatly inconvenience our own ancient ancestors—score humans 1, climate change 0.

Scientists routinely peer back through the mists of time to examine our planet when it was very different from today. Worlds filled with strange and terrible beasts, continents we would not recognize, and temperatures both warmer and colder than today. But even with all mankind's science, the adroit use of proxy data and painstaking study of the layers in Earth's crust, we still do not know exactly how our species spread across the face of this world to become the planet's dominant life-form. We are not even sure where our species originated. In an accompanying commentary, Jean-Jacques Hublin, of the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology, framed the questions still facing modern science this way:

The expansion of modern humans over the planet is one of the most spectacular events in the course of human evolution. During millions of years, distinctive forms of hominins evolved in parallel and sometimes coexisted in the same regions. Between 60,000 and 40,000 y ago, one species expanded out of its African birthplace and replaced all others. The Neanderthals are the best-known archaic humans to go extinct at this time. In PNAS, Lowe et al. resolve pending issues surrounding the mechanism of this evolutionary drama. Their study also fuels an increasing number of questions on the antiquity of the modern human colonization of Eurasia.

What caused the major shifts in recent human evolution has been the subject of much debate over the last 100 years, with climate change a popular explanation. Ice-core records from Greenland have shown that dramatic climate change can occur in as little as 20 years or less. Yet, it would seem that this AET was not a world changing event for either Neanderthals or humans.

Given the dire warnings regarding how supposed anthropogenic climate change will adversely impact humanity, how humans responded to such ancient environmental changes has practical meaning for today. Our human ancestors took a mighty blow from the CI mega-volcano, and managed to live through the sudden cooling that is thought to have followed. In this light it would appear that concern over rapid climate change becoming the downfall of mankind is a bit overblown.

Critics may say that this event was a cooling and AGW is going to cause a rise in temperature, but that ignores the fact that the episode examined above was well before that last glacial maximum. Humanity has since been subject to rapid warming during the Holocene deglaciation starting ~14,000 years ago, including the dramatic reversal and then rebound of that warming during the Younger Dryas. The evidence is clear, if the only future calamities that befall us are due to climate change, humanity will still be standing 1,000 years from now.

Be safe, enjoy the interglacial and stay skeptical.

Current Evolution and De-Evolution

Looking around in Naples, Florida, I can see why we have over-population and pollution problems. The elderly. Humans are living far longer than they used to and we are constantly developing new ways to survive longer un-naturally. Whether or not this is part of our evolution or De-evolution is debatable in my mind. I would be curious to see what everyone else thinks.

I will be postings a more complete form of my thoughts on my blog soon. I would love more thoughts to participate.

Thanks y'all,

-Rick

www.cinesan.com

Deglaciation

Doug....I always thought the temperature dropped quite a bit 20,000
years ago, that it took about 8000 years to melt all that two miles
of ice sbove Wisconsin, as well as from the south pole to some 50
degrees north, and THEN Homo sapiens "started " his civilization.
You use 14,000 for some reason.
Vern Cornell

The last glacial maximum

You have the date for the last glacial maximum right, about 20,000 years before present (ybp, with “present” being officially set at 1950 AD). That was the peak of the glacial period, called the Wisconsinan in North America, the Weichsel in Europe. Since the maximum, glaciers have been in general retreat and the climate warming. That is not to say that there were not oscillations with both cold and warm temperature excursions, warm being a relative term. Two different types of abrupt climate shifts, called Heinrich and Dansgaard-Oeschger events, occurred repeatedly throughout most of the previous glacial period. On a whole, the deglaciation followed the more or less accepted glacial-interglacial cycle of long slow cooling terminated by rapid warming and melting (in geological terms, not from a human lifetime perspective). The previous interglacial was the Eemian, which peaked at roughly 125,000 years ago and was warmer than the Holocene.

The Holocene epoch is identified with the current warm period, known as MIS1. Based on past evidence, it can be considered an interglacial in the current ice age, called the Pleistocene after the previous named epoch. According to the International Commission on Stratigraphy's International Stratigraphic Chart, the Pleistocene epoch ends and the Holocene starts 11,700 ybp. Most people round off to 12,000 years ago for the start of the Holocene warming but things were warming and ice was melting well before that. I used 14,000 ybp as a convenient mark for when real global warming became serious. By that time H. sapiens had already spread to the Americas and established villages across Africa and Eurasia, even though there was still a lot of ice around. There were still a number of dips in temperature on the way to the balmy climate of the Holocene Climate Optimum, a ~6,000 year long period when temperatures were warmer than today.

In retrospective, the Holocene should probably not be an epoch but just another interglacial break in the ongoing Pleistocene Ice Age. There is a great deal of variability in the duration and intensity of interglacial warmings, but during the last half million years they tend to average about 15,000 years, with glacial taking about 100,000 years. The glacial-interglacial cycle is driven by variation in Earth's orbital parameters (the Milankovitch Cycles). An article in Nature argues that the current interglacial might be most analogous to a previous interglacial, associated with MIS11, that lasted 28,000 years. According to some, predicted changes in orbital forcing suggest that the next glacial period won't begin for another 50,000 years. Others have stated that we would be starting the descent into a new glacial now if not for human caused climate change (one reason to hope that anthropogenic global warming is for real). None of us will live to verify these predictions because nature acts on timescales that far exceed human longevity.