Wednesday, July 10, 2019

Paleoclimatology 101 - The Great Meltdown.

Figure One - South of the Ice. 
In my first article on the ice age, I discussed the orbital theory (Milankovitch Theory) behind the creation of Pleistocene ice ages. In my second article, I explored North America during the height of the Wisconsin Ice Age, at the Last Glacial Maximum (LGM) around 18,000 years ago. In this article, I discuss what happened in North America when the ice sheets began to melt.

The Cordilleran and Laurentide ice sheets altered both land and sea geography and profoundly affected the climate and environment in North America. 
Figure Two - A map depicted the area in North America covered 
by the Cordilleran and Laurentide ice sheets 
and the new coastlines at the LGM.  
With four hundred feet of water from the oceans locked up in ice sheets on land and sea, there was more coastline for humans and animals to explore and inhabit around North America. Unfortunately, there wasn't much interior land in Canada or the northern US that wasn't buried under ice. Figure two depicts North America and where scientists believe the ice sheets were located at the height of the LGM around 18,000 years ago. Note the borderline of the United States now and how far land extended out onto the continental shelf during the LGM.   
In my second article, I explored the Last Glacial Maximum (LGM), or what scientists believe was the height of the Wisconsin Ice Age, around 18,000 years ago. It was not long after the LGM, perhaps around 17,000 years ago, that the Cordilleran and Laurentide ice sheets started to melt. It was a slow melt and scientists believe it took around twelve thousand years to melt most of the two ice sheets. After all, these were not your average, normal-sized, run-of-the-mill glaciers. The two ice sheets covered over a million square miles! Scientists estimate the thickness of the ice sheets from around a half a mile thick along the southern edges to over two miles thick in the middle and northern part of the ice sheets. The ice sheets were so heavy that they compacted the Earth's crust down around one thousand feet! 
According to the Milankovitch or orbital theory, the melting began because of the orbital cycle that allowed higher volumes of summer insolation (radiation from the sun) in the northern hemisphere. In my first article, I explained that for ice sheets to grow, they require less summer insolation which allowed ice from previous winters to survive and not melt during summer heat. By adding more ice year after year, decade after decade, century after century; the ICE SHEETS CAN GREW!    

Figure Three - the first book in my
prehistoric book series that took
place after the last ice age.
CLICK this Link!!
By 13,000 years ago, the Laurentide ice sheet had decreased in  area by at least twenty-five percent and by volume by at least fifty percent. During this time, most of the meltwater from the Laurentide ice sheet was flowing down the Mississippi River drainage system causing flooding along river banks and eroding sediment as a massive flow of water advanced toward the ocean. Once the sediment-laden water reached the calmer sea, sediment settled out and formed a massive delta along the coastline. At the same time sea levels were rising, flooding river valleys with water and more sediment. Once the weight of the ice sheets was removed from the coastlines of Alaska and British Columbia, the land decompressed and rose in elevation.
One question often asked; how fast did sea levels rise? One estimate stated that sea levels across the globe rose 110 meters (361 feet), or 1.1 meter per century (3.6 feet per century) between 16,000 to 6,000 years ago. This was at a slow enough rate for humans and animals to adapt to the new environment. As a comparison, sea levels today are estimated to be rising 10 to 20 centimeters (.33 to .66 feet) per century. 

During the great meltdown, water was everywhere, including the parched desert basins of the American west. In the Great Basin of Nevada, California, Idaho, Oregon, Utah, and parts of Wyoming, there were over 100 freshwater lakes. Diversion of the jet stream to the south of the ice sheets in Canada, caused heavy rainfall from the Pacific on the deserts. Add in the meltwater from the ice sheets and lakes formed all over the Great Basin. With no outlets and low evaporation rates, some of the lakes grew gigantic enormous. 
One ice age lake example was Lake Bonneville which covered a good portion of Utah. Lake Bonneville was 19,000 square
Figure Four - Lake Bonneville compared to
size of Utah. 
miles and had a depth of over 1000 feet (figure four). Death Valley even carried water during the ice age meltdown. Further east, wind squalls roaring off the ice sheets, sandblasting the land. Since cold air is denser than warm air, the squalls blew down the slopes of the ice sheets creating gusts of wind up to 100 miles per hour. During the winter when the soil near the ice sheets was dry, the winds carried sand and silt in great dust storms across the great plains, creating 35,000 square miles of sand hills in north central Nebraska and South Dakota. Today, it is estimated that silt from the ice ages covers thirty per cent of the United States, now mostly hidden under forests and grasslands.
One of the great floods of all time happened during the meltdown of the ice sheets. A lobe of ice from the Cordilleran ice sheet served as an ice dam for Lake Missoula, a 3000 square mile ice age lake in what is now the Clark Fork Valley in Idaho (figure five). When the Cordilleran ice sheet melted, so did the lobe of ice that held the waters back at Lake Missoula. When the rising level of meltwater breached the weakening ice dam, it failed and a wall of water and ice, as much as 600 feet high, flooded Idaho and eastern Washington on its way down the Columbia River to the Pacific Ocean. The flood lasted for a month and created the scarred Channeled Scablands in eastern Washington. On the other side of Canada, Lake McConnell and Lake Agassiz raised their own havoc.    

Figure Five - a depiction of what the ice dam at Lake Missoula might
have looked like.  
Even after the great meltdown, the ice age had one more gasp. Around 12,900 years ago in a period called the Younger Dryas, a sudden and dramatic drop in temperature occurred in North America, returning us to the climactic conditions of the Last Glacial Maximum. The great plains returned to the cool, wet glacial conditions, reminiscent of the Wisconsin Ice Age. This cold period lasted for over one thousand years! 
The Younger Dryas is important for another reason; it marks the end of what some archaeologists believe to be the Clovis Paleoindian culture in North America. Some investigators believe that the Clovis culture was wiped out by an extraterrestrial event which triggered the Younger Dryas while others believe the Clovis culture ended in a more traditional manner. I will explore this in my next article. 
Figure Six - Author John Bradford Branney. See all of his
books at John Bradford Branney Books

If you missed my first two paleoclimatology articles, here are the links.  
Hey, and check out my books, OK?  
Milankovitch Ice Age Theory
Last Glacial Maximum

Monday, June 24, 2019

Paleoclimatology 101-Part Two-Last Glacial Maximum

Figure One - North American Paleoindians surviving after the Last Glacial Maximum.  
In my first article on paleoclimatology, I discussed a concept called the Milankovitch Ice Age Theory which explains why ice ages occur and how often their cycle occurs. In this second article, I am writing about what North America looked like during the Last Glacial Maximum (LGM) of the Wisconsin Ice Age. If you missed my first article, here is the link, but be sure to come back after you read my first article;  Paleoclimatology 101 - Milankovitch Ice Age Theory   

According to scientists, the Wisconsin Ice Age reached its Last Glacial Maximum (LGM) sometime between 20,000 and 18,000 years ago. To keep things simple, I am using 18,000 years ago for the LGM in this article. There were probably several advancements and retreats of the ice sheets during the Wisconsin glaciation, but ice sheets and glaciers are very destructive forces. They tend to wipe out everything that gets in their way and previous evidence for advancing and retreating cycles. 

My focus is North America for this article, but readers need to be aware that the last ice age impacted other countries and continents in the northern hemisphere. Figure two is an excellent illustration of the vastness of the last ice age. The map looks down from the North Pole. The areas in blue show the extent of the ice sheets on land and sea. There were places where the ice sheets were as much as three kilometers thick!        
Figure Two - Looking down from the North Pole and showing in blue the 
land mass covered in ice and snow during the last ice age.  
Contrary to social media, fake news, and popular belief, the climate has always been in a state of flux throughout Earth's multi-billion long history, long before humans ever took a step on this planet. Evidence indicates that the Pleistocene, the geologic period of the last ice ages, was a particularly volatile time. Although there have been several events in the geologic past which caused catastrophic climate change, much of the  climatic cycles are related to how the Earth rotates around the sun, and that is the case for the ice ages. 
During the LGM, thick ice sheets covered most of Canada and portions of the northern United States (Figure Three). The massive ice sheets altered geography, climate, and environment on both land and sea. Scientists named the two largest ice sheets covering much of North America, Cordilleran on the west and Laurentide on the east. The Cordilleran and Laurentide ice sheets had a tremendous impact on North America's climate. The water for the these ice sheets was borrowed from the oceans. Scientists believe that to accommodate the estimated size of the ice sheets, global sea levels dropped approximately 120 meters, or 400 feet. The sea level drop exposed the continental shelf around North America and created a land mass northwest of Alaska called Beringia. These new landmasses became available for habitation by animals and humans. There are probably many submerged "Prehistoric Atlantis colonies" on the continental shelf now that sea levels have risen.   
What was it like in North America during the Last Glacial Maximum? It was much colder. 
Figure Three - Key elements of North America during the Last 
Glacial Maximum (LGM). 
Scientists estimate that the presence of the ice sheets may have caused global temperatures to drop nine to twelve degrees Fahrenheit. And though not all scientists agree with the effect on the tropics, some propose that temperatures may have dropped an average of five to nine degrees Fahrenheit. Of course, the closer to the ice sheets, the more the temperature drop. I have seen temperature estimates of eighteen to twenty-two degree Fahrenheit lower than today along the ice sheets and thirty-seven to forty-one degree Fahrenheit drops on top of the ice sheets. The ice sheets were so massive that the jet stream split and went around them. The ice sheets created a high pressure atmospheric zone above them where anticyclonic winds circulating clockwise. These winds were probably fierce and destructive.  
The terrain along the southern margins of the ice sheets was most likely tundra-covered periglacial land resulting from seasonal thawing of snow in areas of permafrost where the runoff, refroze into ice wedges and other structures. Further south from the ice sheets, scientists believe that there were vast spruce forests from the Rocky Mountains to the East Coast of the United States with  interspersed loess and sand hills (Figure Four).  
Figure Four.

 Around 17,000 years ago, the ice sheets began to melt. The northern hemisphere began receiving more summertime insolation from the sun caused an overall reduction in ice sheet thickness and expanse (see Milankovitch Theory). In North America, when the Cordilleran and Laurentide ice sheets melted, it created a mess. Huge lakes formed and oceans received a huge influx of icy freshwater and icebergs, affecting the ocean current circulation patterns. By 15,500 years ago, the ice sheets had melted enough to raise sea levels high enough to create the Bering Strait, but not enough melting to open the ice-free corridor between the Cordilleran and Laurentide ice sheets. It would be hundreds of years later before humans and animals could survive the flooded and boggy passageway. Survival for humans in the ice-free corridor required food, clothing, and firewood availability. 
For decades, scientists believed that the first humans into America migrated through the ice-free corridor between the Cordilleran and Laurentide ice sheets at around 14,500 years ago. However, evidence gathered in the last two decades, indicates there were humans south of the ice sheets, perhaps as early or earlier than the Last Glacial Maximum. So, where did these humans come from? I will cover that story on another day.      
For my next article on Paleoclimatology, I will discuss the Younger Dryas, a period of rapid cooling in the late Pleistocene from 12,800 to 11,500 calendar years ago. It followed closely on the heels of a dramatically abrupt warming that brought the last Ice Age to a close around 17,000 calendar years ago. In the meantime, check out my prehistoric adventures, you will be glad you did! 

                                                          CLICK for INFORMATION

Wednesday, June 5, 2019

Paleoclimatology 101 - Milankovitch Ice Age Theory

Figure One - Ice Age Man. Courtesy of Manhattan's
Museum of Natural History.  
During the Pleistocene, massive sheets of ice flowed southward across Canada into the northern United States about seventeen times. This lasted approximately 1.65 million years. 

Imagine what Canada and other northern hemisphere countries were like with a mile or so of ice on top of the land for thousands of years. The ice sheets were heavy enough to push the Earth's crust down about 1000 feet. Where did all the water for the ice come from. Answer: the oceans! Sea levels dropped substantially. 
Do we know what caused these Ice Ages? Let me present one theory.  
Figure Two - An estimate of the depth of ice in meters
 from the Wisconsin glaciation around 21,000 years ago. 

During the last Ice Age, ice sheets spread and shrank on a 100,000 year-long-cycle. Glaciers dominated the land from 60,000 to 90,000 years during the cold phase of the cycle, and then mostly disappeared for 10,000 to 40,000 years during the warm phase of the cycle (Bonnicksen 2000; p. 5). 
The Wisconsin glaciation began about 100,000 years ago in North America and ice sheets reached maximum thickness around 18,000 years ago. A warming trend started around 17,000 years ago and the ice sheets began to melt. There was a lot of ice to melt. Figure Two represents an estimate of how thick the ice sheets were in meters on four future North American cities. It took another 11,000 years for Canada to completely thaw out, right around 6,000 years ago. Earth has been in an interglacial climate ever since.  
Several things influence climate; the sun’s energy output, carbon dioxide levels, and ocean currents. All of these are important, but the single most important factor in driving our climate is insolation, or the amount of solar energy that reaches the Earth from the Sun. If you don’t believe that the sun has that much influence, try living in Alaska in the middle of winter.

Researchers have found that the sun’s output varies, and that the amount of sunlight that reaches certain parts of the globe is affected by how the Earth orbits the Sun. A Serbian astronomer-
Figure Four - Milutin
mathematician by the name of Milutin Milankovitch (1879-1958) hypothesized that past glacial cycles correlated to cyclical changes in insolation, and that the Earth’s circumnavigation around the Sun were the main cause of these cyclical changes in insolation. Milankovitch and others claimed that the Earth’s orbital path had a huge impact on past global cooling and warming cycles. Milankovitch tested his theory against temperature data from the paleoclimate records, and then he proposed a 100,000 year-cycle between ice sheets. He claimed that the ice sheets were not created by dramatic changes in the amount of insolation reaching Earth, but how solar energy was distributed on Earth. He identified three circumnavigation cycles that were responsible for the Ice Ages.
The cycles were eccentricity, axial tilt or obliquity, and wobble or precession.
Eccentricity. Milankovitch defined the first circumnavigational cycle as eccentricity or the shape of the Earth’s orbit around the sun. Due to gravitational pull from other planets, the Earth does not orbit the Sun in a perfect circle. The Earth has an elliptical orbit around the Sun that varies from five percent to zero percent ellipticity over a 100,000 year-long-cycle (Figure Five). An elliptical orbit reduces or increases solar radiation during the various seasons. When the Earth is in its most elliptical orbit, it receives twenty to thirty percent more solar energy at its perihelion (Earth is closest to the Sun) than its aphelion (Earth is farthest from the Sun). Currently, Earth is in an interglacial cycle and its eccentricity is at a minimum.
Figure Five - Eccentricity. The Earth moves in a slightly elliptical
path during its annual revolution around the Sun.  
Axial tilt or Obliquity. The second circumnavigational cycle proposed by Milankovitch was axial tilt or the inclination of the Earth’s spinning axis in relationship to its orbital plane around the Sun. English, please? Earth orbits the Sun at a different angle than the angle the Earth rotates on its own axis (Figure Six). Earth’s rotational axis is currently at an angle of 23.4 degrees from its orbital plane around the Sun. Milankovitch calculated that the Earth’s rotational axis and its orbital plane around the Sun varied from 21.5 to 24.5 degrees over a 41,000 year-long-cycle. Axial tilt or obliquity creates our seasons. When there is less of an axial tilt, the Sun’s solar radiation is better distributed between summer and winter with increased differences in radiation between equatorial and polar regions. His  hypothesis claimed that a smaller axial tilt angle promotes the growth of ice sheets because warmer winters hold more moisture and produce more snowfall while cooler summer temperatures mean less ice melt. Therefore, ice sheets can grow!      
Figure Six - Axial Tilt or Obliquity. The Earth is tilted on its rotational axis
23.4 degrees from a plane perpendicular to the surface over
which it moves during its revolution around the Sun.  
Precession or Wobble. Some years ago, scientists proposed that the Earth’s axis wobbled due to lunisolar forces, changing the orientation of the rotational axis of the Earth. This wobble as Earth spins on its axis is very slow and is on an approximately 23,000 year-long-cycle (Figure Seven). The Earth wobbles enough to change from pointing at the North Star (Polaris) to pointing at another star called Vega.
Figure Seven - Precession or wobble. The effect of the wobble is to
systematically change the timing of the solstices and equinoxes
relative to the extreme positions the Earth occupies on
its elliptical path around the Sun.  
When the Earth’s axis points at Vega, the Northern Hemisphere winter and summer solstices coincide with aphelion (Earth is farthest from the Sun) and perihelion (Earth is nearest to the Sun), respectively. Winter occurs when Earth is farthest from the Sun and summer occurs when Earth is nearest the Sun, leading to the greatest seasonal contrast. In the Northern Hemisphere, winter will end up in July and August, and summer in January and February during the 23,000 year-long-cycle. This happens because axial tilt or obliquity still accounts for the seasons; summer when that hemisphere leans toward the Sun and winter when that hemisphere leans away from the Sun.

Bottom Line. Milutin Milankovitch suggested a combination of conditions that were conducive to glaciation. The first condition is minimal axial tilt or obliquity. Changes in axial tilt has very little effect from solar radiation at lower latitudes, but increases the effect toward the poles. As axial tilt increases, summer radiation increases significantly. Therefore, minimal axial tilt is conducive to ice sheet buildup The second condition is a relatively high eccentricity. Eccentricity variations affect the intensity of the seasons because it alters the distance the Earth is from the Sun. The third condition is the Northern Hemisphere summer should coincide with aphelion (Earth is farthest from the Sun) creating cooler summers which means less melting of the existing ice sheets. When all of these conditions converge, we have what is often referred to as a "cold orbit" and there is a good chance that ice sheets will expand.       
2000    Bonnicksen, Thomas M. America’s Ancient Forests from the Ice Age to the Age of Discovery. John Wiley and Sons. New York.

2015    Bradley, Raymond S.  Paleoclimatology - Reconstructing Climates of the Quaternary. Third Edition. Elsevier Publishing. New York.   

Tuesday, May 7, 2019

Radiocarbon Dating - Part Two - Reporting

Figure One - A handful of Folsom dart points, surface found on private land in the high plains. 
Age is around 10,900 to 10,200 BP. John Branney Collection.    
Welcome to Part Two of my article on Radiocarbon Dating. In Part One, I discussed how the radiocarbon date process worked. In Part Two, I explore how radiocarbon dates are reported in archaeological papers and journals. 

If you missed Part One, click the link to that article; Radiocarbon Dating - Part One - Process . And don't forget to return to Part Two!          

“Radiocarbon dates indicate that Folsom may have had a relatively long residence in the Rocky Mountains and adjacent Plains from about 10,900 to 10,200 BP.

“At the Hell Gap site the investigators defined a Midland level with dates estimated between 10,700 and 10,400 RCYBP (Irwin-Williams et al. 1973).”
                                 -   Marcel Kornfeld, The First Rocky Mountaineers, page 46

When you read the above passage from Dr. Kornfeld’s archaeological book, do you see anything unusual in the way he reports the ages of Folsom and Midland? Do you get an idea of how old the Folsom prehistoric culture was? Do you know what BP means? Do you get an idea of how old the Midland prehistoric culture was? Do you know what RCYBP means? By the time you read this article, you will be able to answer these questions.   
Figure Two CLICK to ORDER the SERIES
In Part One of Radiocarbon Dating, I mentioned certain “gotchas” that archaeologists and scientists must be aware of when using the radiocarbon dating process. One of the bigger problems is that the amount of carbon-14 isotope in the atmosphere was not constant throughout prehistoric time. At different times during the Earth's prehistory, plants absorbed different amounts of the carbon-14 isotope and since the carbon-14 isotope is the basis for measuring age with the radiocarbon dating process, this is a major problem. The radiocarbon model must know how much carbon-14 isotope was available in the atmosphere at a specific time so it can calculate how much radioactive carbon-14 isotope has decayed. 

Scientists recognized this problem early on in the radiocarbon process and went about solving it. They used dendrochronology, or the study of tree rings, to tie tree rings to the level if carbon-14 isotope levels. Using 4,500-year-old bristlecone pines in the Sierra Mountains, scientists determined carbon-14 isotope levels at the time the rings were made by the trees. The scientists then correlated the rings from living bristlecone pines to dead stumps of trees, allowing the scientists to calibrate to around 8,200 years ago. With this information, scientists created a first pass of “calibrating" the raw radiocarbon age to calendar age.   
Figure Three - Paleoindians, waiting their turn
at the cafeteria. 
To accommodate the lack of certainty in radiocarbon measurements, scientists added an error factor to the measured radiocarbon age. For example, an archaeological report might read that the age of a site is 10,000 ± 160 B.P. This means that there is a 67 percent chance (one standard deviation) that the real age of the site is 160 years plus and minus on either side of 10,000 years before present (B.P.). Whenever you see Before present or B.P. or BP, it means it is measured from the baseline year of 1950. For the above example, if we want 95 percent accuracy, we must use two standard deviations, so we add two times 160 years, or 320 years to either side of 10,000 years before present (B.P.).         

Archaeologists and scientists oftentimes publish uncalibrated or uncorrected radiocarbon ages, even though uncalibrated radiocarbon ages are misleading and do not tie well to calendar years. For example, 9,000 uncalibrated radiocarbon years corrects to approximately 10,200 calendar years after calibration(see Figure Four). And 11,000 uncalibrated radiocarbon years corrects to approximately 13,000 calendar years; two thousand years of correction! When you see an author quote that Clovis at 11,000 radiocarbon years, it is really around 13,000 calendar years. That is a big difference.  

Most of us think in calendar years, not radiocarbon years. We want to know how old a site or an artifact is in calendar years, not in something as esoteric as radiocarbon years. 
Figure Four - One representation of radiocarbon age conversion 
to calendar age. Enter the vertical axis with an uncalibrated 
radiocarbon age and read the calibrated calendar age 
on the horizontal axis.    
So why do archaeologists and scientists report uncalibrated radiocarbon age instead of calibrated calendar age? I asked that same question to a practicing archaeologist and he told me "because archaeologists write their reports for other archaeologists, not for lay people". I thought his answer was snobbish. I don't think he recognized how condescending his answer was. I mentioned to him that many of us "lowly lay people" are interested in early man and read these reports. I saw this as further evidence of the brick wall that exists between professional archaeologists and avocational archaeologists and collectors.    
Another reason that archaeologists and scientists might report uncalibrated radiocarbon age is that they do not have a high level of confidence in the calibration model or results. After all, models assume a certain amount of carbon-14 isotope in the atmosphere at a certain time. That is a big assumption. 

I became interested in archaeology over fifty years ago and since then I have seen the proposed ages of certain prehistoric cultures change over time. I assume this is because radiocarbon dating models and sampling methodology have improved. I remember when Clovis technology was advertised as around 11,000 years old and now scientists are reporting a better age for Clovis is 13,000 years. I am sure these reporting discrepancies come from improvements in technology, sampling methodology, and computing power.    
When you read archaeological reports, be sure to note what radiocarbon dating nomenclature they are using. Uncalibrated radiocarbon age can be reported in RCYBP (Radiocarbon Years Before Present), C14 ka BP, 14C ka BP, 14C ka BP, radiocarbon years, c14 years before the present, rcbp, carbon-14 years before the present, and CYBP. In all cases, B.P. refers to the baseline year of 1950. Again, if you see this nomenclature behind an age, the age is an uncalibrated radiocarbon age. It is my experience that authors of archaeological site reports don’t explain whether they are using calibrated or uncalibrated radiocarbon age. Readers must figure this out on their own. So, readers be waryUncalibrated to calibrated radiocarbon dates makes a huge difference in ages as you saw above.  

The most common abbreviation for calibrated radiocarbon age is cal B.P., cal yr. BP, B.P. or the one I like the most; XYZ is blankety blank blank years old. 
Figure Five - A handful of Midland dart points surface found on private land in the high plains. According to the 
radiocarbon age nomenclature used by Marcel Kornfeld, Midland is close to two thousand years older than Folsom. 
We know better, Folsom and Midland technologies were contemporaries. John Branney Collection.      

Let me return to the original passage at the top of the article from The First Rocky Mountaineers by archaeologist Marcel Kornfeld. On page 46, Dr. Kornfeld discussed the ages of the Folsom and Midland prehistoric cultures. Most people contend that the Folsom and Midland prehistoric cultures happened pretty much simultaneously. Some people believe the same people made both Folsom and Midland.    
Radiocarbon dates indicate that Folsom may have had a relatively long residence in the Rocky Mountains and adjacent Plains from about 10,900 to 10,200 BP.
At the Hell Gap site the investigators defined a Midland level with dates estimated between 10,700 and 10,400 RCYBP (Irwin-Williams et al. 1973).

It appears from this passage that Dr. Kornfeld mixed uncalibrated radiocarbon age nomenclature, RCYBP in the second paragraph, with calibrated radiocarbon age nomenclature, BP in the first paragraph. By doing this, he is stating that the Midland archaeological level was around 12,620 calendar years old, close to two thousand years older than Folsom. We know better, so I have to assume Dr. Kornfeld meant to use BP for Midland and not RCYBP

Mistake? Probably. Confusing? Definitely, even for the "experts". Be careful when you read radiocarbon ages in archaeological journals and articles! I hoped you learned something. I did when I did the research for this article.   


Friday, April 12, 2019

Radiocarbon Dating - Part One - The Process

Figure One - Three inch long Montana Clovis point made from a multi-colored jasper.
How do we know who old Clovis points are?  John Bradford Branney Collection.  
In Part One of my series on radiocarbon dating, I present the overall radiocarbon dating process and some of its pitfalls. In Part Two of my series, I will present how these radiocarbon dates are reported in archaeological site reports. My intent is to share the information that I learned during researching the topic. It is not my intention to cover all the nitty gritty little details of the radiocarbon dating process, but to give my readers enough information for a basic understanding and appreciation of the process. I have found that the radiocarbon dating process is a lot like sausage making; you can generally understand how sausage is made, but the less information you have about the ingredients, the better.   
Figure Two - CLICK for the SERIES
I have read a ton of books and reports on archaeological sites, especially about the Rocky Mountain region. I read these books and reports because I am interested in archaeology and I want to know more about my own prehistoric artifact collection. I also do research for the books I write, such as my prehistoric adventure book series entitled the SHADOWS on the TRAIL QUADRILOGY (figure two). 

It has always baffled me how archaeological books report the radiocarbon dates for sites. It seems that every author uses different phrases and nomenclature when reporting a site's radiocarbon date. For example, these are two reported dates; 10,000 RCYBP and 10,000 years BP. Do they mean the same thing? Are these sites 10,000 years old? The answer is no. The first date is an uncalibrated radiocarbon date and the second date is a calibrated radiocarbon date (don't worry, I will discuss this later). I seldom see an author report the age of an archaeological site in simple terms that everyone can understand, such as "this site is 10,000 years old".   

What do you know about the radiocarbon dating process? Radiocarbon dating has become indispensable in archaeology. Almost every archaeologist uses radiocarbon dating in one way or another. If we understand the basics of the radiocarbon dating process, it helps us to understand the dating methodology in archaeological books and reports. As consumers of these reports, we need a general understanding of the process and its strengths and weaknesses.
Figure Three - How the radiocarbon dating process works. 
Radiocarbon dating is one of the most widely used methods for scientists to determine the relative ages for biological specimens, such as wooden artifacts or bone. The process uses a natural phenomena occurring in the Earth’s atmosphere (figure three). When cosmic rays from the sun bombard nitrogen atoms in our upper atmosphere, an unstable, radioactive carbon isotope called carbon-14 is created in the upper atmosphere. This carbon-14 isotope oxidizes into a carbon-14 dioxide isotope which settles in the lower atmosphere. Plants and algae take in this carbon-14 dioxide isotope at the same ratio that it exists in the atmosphere. Other living organisms within the food chain also exchange carbon with the atmosphere through respiration and by eating other organisms. These organisms incorporate the carbon-14 isotope into their tissue at the same ratio as the atmosphere. 

When an organism dies, its carbon intake stops and the radioactive carbon-14 isotope in its tissue starts to decay into stable carbon-12 isotope. Radioactive decay is the process by which an unstable atomic nucleus loses energy (in terms of mass) by emitting radiation. The carbon-14 isotope has a radioactive half life of approximately 5,730 years, which means in 5,730 years half of the carbon-14 isotope in the dead organism has decayed to a stable carbon-12 isotope. To come up with an age for the dead organism, archaeologists and scientists test its remains for the presence of the unstable carbon-14 isotope and its ratio to the stable carbon-12 isotope. Wood and charcoal are the best materials to use for the process, but other once-living materials will work, as well.
Figure Four - Paleoindians 
Radiocarbon dating is probably the most reliable tool in the tool box for dating archaeological sites, but the process has a few challenges we should be aware of. The first challenge for the archaeologist is to find a reliable and uncontaminated sample within the cultural material that is of interest. The archaeologist must ensure that the sample tested is associated with the cultural material in question, and that the sample is not contaminated with unrelated organic deposits. For example, testing a piece of charcoal from a prehistoric fire hearth in a geologic horizon where there is clinker coal deposits from an earlier geological episode.  

The second challenge is that the site must be less than 50,000 to 60,000 years old. As previously mentioned, the half life of the carbon-14 isotope is 5730 years. If you cut the amount of carbon-14 in half a few times through decay, statistically there is very little carbon-14 left to measure. The line in the sand for an accurate measurement ends at 50,000 to 60,000 years old.   
The third challenge is the biggest hurdle to overcome. In my third paragraph, I explained how cosmic rays from the sun bombard nitrogen atoms in our upper atmosphere, creating the radioactive carbon-14 isotope which is the key ingredient needed for radiocarbon dating. So far, everything is hunky dory; we know the half life of carbon-14 and the amount of carbon-14 produced in the atmosphere. Therefore, we should be able to determine the remaining amount of carbon-14 isotope in our sample and thus its age.  

Unfortunately, it isn't that easy. The big kicker is that the bombardment of cosmic rays from the sun has not been consistent through time, therefore, the production of carbon-14 isotope has not been uniform through time. Throughout geologic time, there were peaks and valleys in the production of the carbon-14 isotope in the atmosphere. As an example, archaeologists believe that between 11,300 to 11,600 years ago, less carbon-14 isotope was produced in the atmosphere than today. This throws everything out of whack. A reduction in the production of carbon-14 isotope results in a flat plateau along the radiocarbon dating calibration curve which results in a difference between a measured radiocarbon years and actual calendar years. Radiocarbon years must be calibrated to calendar years using dendrochronology, and estimates of peaks and valleys in the production of carbon-14 isotope in the atmosphere. Messy is the best word to describe it. This is one of the main reasons some archaeologists report ages in uncalibrated radiocarbon years - it is cleaner to report it that way. 

Confused yet? Don't feel like the Lone Ranger! 
Figure Five - The difference between uncalibrated radiocarbon dates (left axis) 
and calibrated radiocarbon dates (bottom axis).   

The graphic in figure five illustrates my above point. The vertical axis (left-hand) shows the years in uncalibrated radiocarbon years. The horizontal axis (bottom) shows the years in calibrated calendar years from the year 1950. The red curve illustrates a simplified calibration curve. As an example,  10,000 radiocarbon years on the vertical axis is 11,400 calendar years on the horizontal axis. BP is defined as before present and is measured from the baseline year, 1950. 

You can see how this that this can get confusing, especially if some authors report uncalibrated radiocarbon years while others report calibrated calendar years. It is beyond me why the archaeological community has not standardized their reporting criteria for radiocarbon dates. The cynical side of me wonders if the scientists and authors want their readers confused. See you in Part Two of my series and I will show some examples of this confusion. Until then, read my book series, please! 

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Thursday, January 24, 2019

Shadows on the Trail Meets Clovis Wandering

by John Bradford Branney

Figure One - Five High Plains Clovis spear points / knife forms surface found on private land.
Note that each of these points has a flute starting at the center of its base and ending in the body
of the point. Longest point is 3.85 inches long. John Branney Collection.  

Close your eyes and imagine the emptiness of North America thirteen thousand years ago. No cities, no towns, no highways, no planes. Not much of anything except a few bands of roaming Paleoindians spread across the expanse of a continent, living amongst a land of countless animals.
After its discovery and coronation in the 1920s and 1930s in New Mexico, Clovis became the royalty of North American archaeology. Scientists proclaimed the mammoth hunters who made the Clovis artifacts the First Americans, i.e. the first humans to ever walk on North American soil. Clovis technology has taken the breath away from artifact hunters and scientists alike. Books and magazine articles have fulfilled our insatiable appetite for Clovis artifacts and the Paleoindians who made them. No other prehistoric culture or technology in North America has drawn as much attention as Clovis.
Figure Two - Edward Howard at the
Clovis site in New Mexico in 1933.
We know from current archaeological evidence that Clovis technology started showing up in North American sites around 13,500 years ago. Where did the Paleoindians who made this technology come from? The first and the longest held belief was that Paleoindians, originating in Asia, crossed the Bering Strait from Siberia into Alaska during the last ice age when ocean levels were low. Since these Paleoindians were considered the First Americans, they either had to bring Clovis technology with them from Siberia or they had to invent it here. The Clovis First theory held water for decades and there are still a few scientists who hold it dear, but we have yet to come up with the "smoking gun" that proves Paleoindians crossed the Bering Strait bringing  Clovis technology with them.     

When it comes to Clovis technology, what is that smoking gun? Clovis technology is represented in the archaeological record by stone projectile points, prismatic blades, blade cores, and unifacial tools made from blades. Clovis technology was heavy into blade technology. Clovis technology also includes projectile points and foreshafts made from bone and ivory. Clovis technology is also associated with red ocher as these Paleoindians sprinkled the hematite-rich powder indiscriminately over artifacts and burials. Other Paleoindian cultures used the above technologies occasionally, so these were not unique to Clovis. However, there is one technological innovation that had a Clovis signature. The "smoking gun" that distinguishes Clovis from others is the "Clovis flute" on projectile points! 

Clovis projectile points are quite distinct, you might say they are one of a kind. Beyond their distinctive outline and flaking pattern, Clovis projectile points had another special feature; they had a flute or groove, starting at the center of the base and running toward the tip of the projectile point (figures one and three). Artifact hunters and scientists have found fluted Clovis projectile points across the lower 48 states. Artifact hunters and scientists have discovered Clovis or Clovis-like projectile points from coast-to-coast, from Canada to northern Mexico. This was an amazing dispersion of technology over a little more than three hundred years. Adaptation of Clovis technology must have been quick and decisive. Clovis or Clovis-like projectile points are one of the most recognizable projectile point type in North America. If Clovis technology came to North America through Siberia, why can't we trace Clovis technology back to Siberia?
Figure Three - 3.85 inch long Clovis spear / knife form surface
found on private land in Colfax County, New Mexico. Note the
extraordinary flute. John Branney Collection. 
A master flintknapper named Bob Patten once wrote, "If, as it appears, the Clovis tradition [fluting] was invented here [North America], someone must have already been here to invent it."

They say that hindsight is 20-20. To believe that there were no humans in North America prior to Clovis has always seemed na├»ve to me. Every other continent on the globe has evidence of humans going back tens or hundreds of thousands of years. How do we account for North America being human-free until around 13,500 years? How did North America stay isolated from the “Cradle of Man” in Africa for million or so years?
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Ninety years after scientists first documented Clovis in New Mexico, there is undeniable archaeological evidence in North America that Clovis people were not the First Americans. Perhaps, scientists were so locked into their ‘Clovis First’ theory that they poo pooed anything that disputed it. Perhaps, when they dug archaeological sites, they stopped digging once they found Clovis. In the past two decades, the "Clovis First" theory has taken severe blows and is down for the eight count and dead to some of us. Archaeological discoveries older than Clovis are aplenty, pushing human entrance into North America to 14,500 years, 15,000 years, 16,000 years, and beyond. It would not surprise me that some day soon archaeological evidence will prove early man was in North America over 50,000 years ago.
As far as the origin of Clovis technology, the mystery remains unsolved. In 2011, scientists excavated Clovis-like fluted projectile points at a site called Serpentine Hot Springs in northwest Alaska (Figure four). Was this the smoking gun everyone was looking for? Charcoal from the site dated around 12,000 years,  a thousand years younger than Clovis technology in the lower 48 states. If the Clovis-like fluted projectile points in Alaska originated in Siberia as the Clovis First theory contends, then the Alaskan points should be older than Clovis technology in the lower 48 states. Instead, the Clovis-like fluted points at Serpentine are one thousand years younger, possibly indicating that the Clovis technology dispersion direction was from the lower 48 states to Alaska, and not visa versa. 

Bottom line? We still have no smoking gun for the origin of Clovis technology.     
Figure Four -  Fluted points found buried in 
northwest Alaska. Charcoal dated the site
younger than Clovis in the lower 48 states.