Human Prehistory, Ice Ages and Global Warming

I have been having a lot of reading fun recently, expanding my view to the rear.  The books I have been buying are popularized treatments of humanity’s prehistory–recent prehistory, from the period of thirty to fifty thousand years ago to our historical period (something on the order of 5 or 6 thousand years ago).

A topic I have gotten interested in is global warming, mostly because it has been in our country’s consciousness over the last several decades, but also in the last century, going back to the late 1950’s, then peaking again in the middle aughts of this century.

That history of increasing alarm among the scientific community, and its–as usual–inability to convince a skeptical general audience of non-scientists that there was a “there there” had attendant corollaries as well, one of which was newfound attention on the ice ages our world has seen over its long, long past.

That topic interested me because I knew– vaguely and not too specifically–that the conventional scholarly consensus was that the earliest settlement of the Americas had been tied to a period of time in which there was a “land bridge” between Asia (Siberia) and the Americas (specifically, the Alaska coast of North America.

We still today refer to the northern Pacific sea in that area between Asia and North America as the Bering Sea, so it is not a stretch to understand that the “land bridge” was called Beringia, and it existed as low but dry land because continental glaciation (glaciers that built up on land masses) around the northern axis of the globe (in Asia, Europe, and North America) had taken enough water out of the world’s seas and converted into precipitation that fell over cold climates that glaciers were born there that had the final effect of  lowering the levels of the oceans, thereby increasing the shorelines of the world . . . about 400 feet.

Sizable Changes in Sea Level in the Past

Tsumanis, For Example, Change Coastlines Dramatically and Suddenly:
Just a 300 Foot Tsunami On Our East Coast Would Take Out Wash, DC

Now 400 feet up west of Alaska doesn’t sound like much, but if you were to see a picture of what the eastern cost of the US would look like if only 300 feet were inundated by sea water, you would be impressed about how much of the population of our country is actually living very, very close to the danger zone of, say, a tsunami: at just a tidal flood of 300 feet above sea level, Washington, D.C. would be under water, and up to 100 feet of its monuments and buildings.  ALL of Florida would be under water, since it is only between 10 to 14 feet above sea level.  We just have little regard for how close a good deal of our country’s land mass is to disaster by water level, and that extends to our misunderstanding of how quickly a submerged corridor of land could have opened up between northwestern Asia and North America back at the maximum of our last ice age.

Here is a Google Earth image of the area now (today’s image) open water in the Bering Sea:

That light blue shaded area between Alaska and Siberia is the part of the continental shelf now under sea level that is called Beringia when it actually appeared above water level.  The area pictured a darker blue above that underwater shelf is the water that is actually usually under sea ice at and around the North Pole.

My overall point about Beringia, though, is this: it only takes a couple of hundred feet of change in the level of our global oceans to change the size of our continental coastal shelves dramatically.  And that is what happened at the height of the last glaciation (Last Glacial Maximum or LGM), robbing the oceans of the volume to cover lots of coastal shelves around the world.

Another view of where we are currently in this area of the globe is presented by an article that was published in 2012 and a graphic from which is shown at the left: note that the line drawn on the image is the northern continental shelf of Asia, Beringia and Alaska, and the blue above them is the arctic sea, some of it closest to the north pole covered with sea ice, with Greenland’s continental glacial ice abutting it.

These points were all make just to convey to you that the shorelines of the continents touching the Atlantic and the Pacific oceans have varied considerably over a long period of time (hundreds of thousands of years).  And for early human purposes, one of those variations happened to be the appearance of low but dry land between what we think of as the Siberian coast of today and the coast of Alaska today: the Bering Land Bridge, or Beringia.

[One last point: before leaving the larger image above, please note that when the last global ice age was at its maximum (technically, called the Last Glacial Maximum, or LGM), in Europe there was low land between the British Isles and the European continent: there was no English Channel, it was simply another “land bridge” between what we label today as the White Cliffs of Dover and France!  England, Scotland and Ireland were also populated–in this case, from the east–by paleolithic human beings who moved out of Asia and the Middle East into and through Europe into the British Isles (and then into Iceland).]

Natural Forces Leading to Periodic Ice Ages

I found an science article that gave the specific reasons that the earth’s distance from our sun changes, those changes leading to the freezing of precipitation over land: continental glaciation . . .

First, the Earth’s orbit around the sun is not circular, it is slightly elongated.  This orbit changes on a cycle of about 100,000 years.  “When the orbit is circular, the distance between the sun and the Earth stays the same. But when the orbit is slightly elongate, the sun and Earth vary from being farther away from each other (making the climate colder) to being closer together (making the climate warmer).

Second, the earth is tilted off vertical, which gives us our seasons as we orbit around the sun.  However, the Earth’s tilt changes from 22° to 24° and back again about every 40,000 years. Right now, it is tilted at 23.5°. When the tilt is at its greatest, differences in temperatures between summer and winter will be greatest.

Third, Like a spinning top as it is slowing down, the Earth’s axis wobbles in a circle every 23,000 years. Because of this wobble, the Earth moves just a little bit more than one complete orbit each year. So, for example, if the Earth is in one place in its orbit on, say, 1 July, it will be just a little bit further around the orbit on 1 July of the following year. This is called “precession”.

These complications make it hard to visualize, but you can see the variability caused when you look at them over time: there is scientific regularity to these three natural factors of glacial periods in our climate, even though we did not see the perfect cycles we would like to see . . .

At any rate, there is clear evidence, and we have the science to show it, that there are natural causes of changes in our climates around the globe that account for the slow warming or slow cooling that we each experience, over years, living in the same region of the globe.  Ice ages exist, although most humans can’t comprehend them as they occur in cycles that are complicated and much, much longer than “human scale” time periods.

Human Spread on Earth Was a Function of Climate Change

I think it is interesting to view human beings, like other animals, as dependent on their environments and the changing characteristics of those environments.  Clearly we interact with our environments in very specific ways to obtain the fuel we need (what we consume) and to arrange the warmth we require (how we shelter ourselves, how we cloth ourselves).   We are intimately related to our environments, both physical and biological. So I see our ancestor’s relationship with our climate patterns as just another example of how we as a species made decisions about how we could most effectively live our lives and grow our families: adapt or die.

It is fascinating to me that as we developed as a species we moved from one region of the earth to another.  I suppose for different reasons, of course, but high on that list of whys were factors like following our food sources, both animal and plant-based.  It is pretty clear that as a species we were first Stone Age hunter-gathers, locating sources of food that already existed . . . and then setting about to fetch them and eat them.  Animals were sources of food for us, and that involved killing the animals (or finding already dead animal carcasses and feasting off of them), which in turn involved figuring out methods of killing them.

Luckily for us, that process typically included making stone points that were particularly successful in putting together devices that could be hurled or shoved or propelled by crude technologies into the hides of the animals whose meat we wished to eat.  In fact, a good deal of our study of prehistoric humans is labeled by the features of the stone points (arrowheads, spears, axes, etc).

Those worked stone projectiles and cutting tools were the most likely to be found evidence of past civilizations that we find today, sometimes by random passersby in meadows or farmed fields, shorelines, sometimes by thoroughly educated and trained archeologists who know where to look, and how to identify them.

In fact, two specific shapes of stone points are usually mentioned as being typical of the peoples who came to America first: the paleo peoples associated with the making of the Clovis point and the Folsom point.

It is a prehistory that is difficult to follow for several reasons.  As with most changes sciences that deal–not in experimentation but–in observational evidence, explanations (theories) tend to be posited, then evidence (of some form or another) is sought that supports one’s thesis, with this evidence-searching process taking place in what turn out to be non-controlled circumstances.   We can’t complain about the fact that areas of knowledge like planetary science and cosmology, or archeology, can’t manipulate circumstances in order to carry out the ideal model of explanation (a controlled experiment), but we need to understand the assumptions that underlie the explanations we are given for why something should be viewed as supporting or negating one’s theory of how things work.  I’m not “blaming” archeologists for studying a subject with one methodological hand tied behind their backs; they do the best with the evidence they find, because it is evidence about the process they are trying to understand: how humanity developed and spread across the planet!

Other Hypotheses About How the Americas Were Peopled

Lets first recap:

1. The Standard Hypothesis: Asian Routes to the New World

This is the one I grew up with, indeed, that all of us grew up with.  Somewhere in the dim recesses of the past, a group of Siberians move generally eastward, across what we now know was an area above sea level called Beringia, to Alaska and northern Canada, slowing (at still an unknown pace), then moving again to cover the areas of the American west, the midwest and the east of North America, and then also moving down through Central America to South America.

That is the Beringia hypothesis that is marked in RED on the image to the right.

There is (of course) a derivation of that “from Asia” theory called the

2. Coastal hypothesis, which suggests that the first groups moving eastward out of Asia came by water, obviating the necessity of dealing with the continental glaciers still evident  in Alaska and Canada and the lower US states.

The Beringian advocates point out there is evidence of a high land area between the eastern (Laurentian) continental glaciation and the western (Alpine) glacier system that would have allowed the first Americans to migrate south from Beringia by land and not coastal:

Well, those two routes (Beringian Land Bridge, and Coastal Hugging) where the two main ideas about how the Americas got populated when I was growing up.

 3: Polynesians Sailing Eastward to South America

You remember the popular press exploits of Thor Hyerdahl, the Scandanavian explorer whose voyages on Con Tiki staked the claim of Polynesian peoples access to South America as at least another possible route for immigration into the Americas.

Well, interestingly, just a couple of years ago, a French research team showed that there is evidence that the DNA of the sweet potato in the Pacific shows that Polynesians traveled to South America . . . and took back the sweet potato, among other artifacts and traditions.  They . . .

found that the  indicated that the sweet potato had migrated to Polynesia long before European explorers had made their way to that part of the world. That meant that the  had to go get it themselves or it got there some other way, such as via seeds carried in the wind, aboard natural rafts etc. But because scientists have already uncovered proof that Polynesian sailors made it as far as the Easter Islands, it seems plausible to envision they extended their reach to mainland South America as well.

The DNA evidence also showed that another two lines came about as a result of European exploration – originating from South America to Europe and then on to other parts of the world. In the first wave, the sweet potato was carried to the western Pacific, in the second it was carried to the Philippines. Both resulted in further sweet potato migration to their respective parts of the world.

Bob Yirka,Sweet Potato DNA Indicates Early Polynesians Traveled to South America,” Phys.Org, Jan 22, 2013

I should mention that starting back in the 1990’s, there were some alternative suggestions of routes into the Americas coming from Europe thousands of years BEFORE all of the stone point evidence connected with the Beringian / Northern Asian advocates, which was approximately 12 to 14 thousand years ago:

4.  The Iberian Hypothesis: the Solutreans from Western Europe

According to the Solutrean hypothesis, people of the Solutrean culture, 21,000 to 17,000 years ago, in Ice Age Europe migrated to North America by boat along the pack ice of the north Atlantic Ocean. They brought their methods of making stone tools with them and provided the basis for the later (c. 13,000 years ago) Clovis technology that spread throughout North America. The hypothesis is based on similarities between European Solutrean and Clovis lithic technologies.

(fromSolutrean Hypothesis,” Wikipedia)

My Conclusions

I know its been a long, winging trail back through the history of the academic community’s interest in ferreting out and explaining our continent’s settlement beginning sometime in prehistory, but I think it is a story worth following.

It comforts me to see the absolute certainty with which each generation of academics have stabbed their standard into the ground affirming that they now have the story right: thus and so happened, and here is our evidence of it.

If you follow this whole story, you see something interesting happening along the way though: new disciplines have been folded into the process of answering the same old question: when did the New World get explored and settled, and what were the cultural and social habits of those unknown peoples.

At first, it was archeologists, who were focused on what they could learn from stone tools they saw, then on what the bones of these first Americans left in their burial sites that could tell us about them.  Soon radio carbon dating was added to the mix, using geologic stratigraphy to “place” an artifact in time.

Next, historical linguists added a new source of independent evidence, constructing trees of word changes in language groups that were assumed to change at standard rates over time, showing the relationship and ancestry of one group of humans with another.

Finally, we had seen genetic/DNA evidence added to the mix.

Just out of nowhere, let me now ask this question about how the process of collecting evidence in this subfield of anthropology, archaeology, has changed in the life of scholars who entered the field in, say, 1970?

I’ll answer it this way:  I’ll bet you the faculty who taught the graduate courses taken by the new Ph.D. in archaeology in 1970 would have some difficulty deciphering the contents of a number of the articles in the latest issue of a standard journal title used to disseminate new findings in the 1970’s to archaeologists.   So, what I did was go to a standard source of abstracts to articles, papers and books in anthropology (Abstracts in Anthropology), and found abstracts of an article today and one in 1970.  The earlier one was about dendrochronology–you know, tree rings indicating annual growth; the second was about soil chemistry in an area of tundra.

Two Articles from Abstracts in Anthropology, Archaeology Section:

1970 Abstract: Dendrochronology (Tree Rings)

Jeffrey S. Dean.

Thirteen Pueblo III sites of the Tsegi Phase (dated from A.D. 1250 to 1300) in the Marsh Pass area of northeastern Arizona are the focus of several experiments designed to evaluate the contributions of dendrochronological studies to archaeological analysis. This involves the derivation of three types of information from archaeological tree-ring collections: (1) chronological data permitting the assignment of absolute dates to units of archaeological analysis; (2) data on cultural practices and specific historic events; and (3) data on past environmental conditions. Two large “cliff dwellings,” Betatakin and Kiet Siel, were intensively sampled for tree-ring material, with the objective of 100% samples of the timbers in each site. Samples of 292 tree-ring specimens from Betatakin and 540 specimens from Kiet Siel are. augmented by comprehensive data on the provenience and condition of each timber and by detailed architectural data. Less intensive studies of eleven other Tsegi Phase sites provide a basis for the consideration of the phase as a whole. Analyses of the tree-ring dates, the species assemblages, the nature of the terminal rings, and the prehistoric use of timbers provide the basis for inferences concerning the chronology and internal development of each site; the processes by which the villages were founded, peopled, and abandoned; the social organization of the villages; a number of cultural practices ranging from the use of dead wood to the stockpiling of timbers for future use; changes in the environments of the sites; and the dated history of the Tsegi Phase occupation of Tsegi Canyon. Significant differences between these contemporaneous sites are relevant to the consideration of the dynamics of intraphase variability.

Papers of the Laboratory of Tree-Ring Research #3, The University of Arizona Press, 1969.

2017 Abstract: Ecosystem Soil Analysis

“Variation in N2 Fixation in Subarctic Tundra in Relation to Landscape Position and Nitrogen Pools and Fluxes,” Arctic, Antarctic, and Alpine Research, 48(1):111-125. 2016

Biological N2 fixation in high-latitude ecosystems usually exhibits low rates but can significantly contribute to the local N budget. We studied N2 fixation in three habitats of East European subarctic tundra differing in soil N stocks and fluxes: N-limited vegetated peat plateau (PP), frost formations of bare peat called “peat circles” (PC) with high availability of soil N, and vegetated upland tundra (UT) with low to intermediate N-availability. Nitrogen fixation was measured at field conditions twice during summer 2011 by acetylene reduction assay, and N2 fixation rates were verified by 15N2fixation assay. Response to variation in nutrients, carbon, and temperature was studied in complementary laboratory experiments. Further, we aimed to link N2 fixation rates to N deposition and major N transformation rates (gross and net mineralization, plant N uptake) including high N2O emissions recently found from PC. We hypothesized that N2O emissions in PC were fueled partly by biologically fixed N. Contrary to that hypothesis, N2 fixation was found solely in PP (0.01–0.76 mg N m-2 d-1), where N2 was fixed by moss-associated cyanobacteria and heterotrophic soil bacteria. The low N and high P availability corresponded with the occurrence of N2 fixation in these soils. Nitrogen fixation represented only a small portion of plant N uptake in PP. Conversely, bare PC (as well as vegetated UT) lacked N2 fixation and thus N2O efflux is most likely fueled by release of mineral N to the soil through internal nutrient cycling.

Its tough keeping up with your literature (something a scholar is supposed to do!), when your literature today speaks in a language about new concepts (in new, not personally studied areas of knowledge) you didn’t study then, and don’t know how to think in terms of today!

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