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Part 4: Who were the ancestors of Asians and Europeans?

Page 1: Modern Anthropological Dating Techniques

 
Before discussing the European and Asian ancestors, it is necessary to introduce some methodologies adopted by modern anthropology to determine dates.

Ⅰ.The Uncertainty of Molecular Anthropological Dating

In previous part, we discussed the Y chromosome Adam theory as well as the Mitochondrial Eve theory. Based on these theories one can extend the millennium quest with the use of DNA from modern man to trace his ancestors in the distant past. The principle behind this type of tracing and confirmation of paternal relationship is quite similar. From the standpoint of hereditary lineage, it is both accurate and error free.  However, since DNA mutation is random and the mutation rate is inconstant, it is inaccurate way to determine the year of birth of our ancestors regardless of the way one uses to trace geneology i.e. via mitochondrial DNA or the Y chromosome. To get an accurate time period one needs to rely on anthropological dating techniques.

Figure4-1  5063year-oldbristleconepine

In the dating of some archeological articles, often two dates are given: one being the carbon 14 (C14 years before present ” C14 BP”), and the other being the calendar years (Calendar years before the present, ”Cal BP” or BP ). For example, if the age of the charred wood discovered in a cave is determined to be 12,500 (C14 BP ) and 14,5000 (Cal BP), the former is the result of carbon 14 dating and the latter is the corrected calendar years.

Some people don’t consider the carbon 14 method to be reliable. They believe that our earth and mankind only has a 10,000 year history. However, it is not consistent with scientific facts.

2.The otherdating methods

(1)Uranium dating method

One of the isotopic dating methods is based on the ratio of radioactive uranium nuclides to determine the age of the geological sediments. Commonly used date methods use uranium 234U/238U, thorium-uranium  230Th/234U and thorium-lead 231Th/210Pb.

The principle of measurement is 238U and 235U decay series contain a variety of radioisotopes. In the normal geological processes, Daughterof uranium such as thorium, and lead separate themselves from parent uranium-238U and 235U. And each half-life will determine their respective rate of decay. The body of the mother forms the decay of the daughter nuclides. Radiation detectors can be used to measure the radioactive isotopes ratios in order to calculate the age of the geological sediment. If ancient mankind’s remains and relics in these sediments with the same age as the sediment, then this will represent the times when the ancient people had lived.

This method is suitable for dating the Paleolithic ancient ruins around 50,000 -600,000 years ago. Moreover, this method is limited to the determination of calcium carbonate rich rocks.

 (2)Potassium-Argon Dating Method

Another isotopic dating method is to use potassium 40 which is an unstable isotope. It can decay and become argon 40. Within a stone, argon is in a liquid form and can freely escape. After the stone solidifies, potassium 40 decays to become argon 40 remaining in the stone. Using mass spectrometry instrument one can measure the argon 40 and the remaining potassium 40 ratio. From this ratio one can calculate the age of the mineral crystal and the rock containing potassium. Moreover, one can determine the age by which the rock was formed. The half-life of potassium 40 is 1.25 billion years and thus can be used to determine rocks which were formed over 100,000 years ago. More recently formed rock does not meeting the desired dating accuracy because the argon content is too low. This method is often used to determine geological events in active volcano areas.

 (3)Thermoluminesense (TL) and Optically Stimulated Luminesence (OSL) Dating Methods

Thermoluminesense (TL) Dating method: Quartz crystals in feldspar, calcite, pottery, porcelain and other objects contain lattice crystal structures which can absorb radioactive electrons trapped in the lattice at a fixed rate over time.  The energy in these trapped electrons can be released producing a range of luminescent glows shown as light by heating with just a small sample from the aforementioned objects.

The amount of energy can be measured by the thermoluminescence detection instrument. After subjecting to heating, certain types of electron trapping mechanism become zero. The measured amount of radiation energy is directly proportional to the age of the ceramic.

This is the principle behind the thermoluminescence as a dating method. The TL method dating range varies from several hundred years to one Millionsyears. Its major use is in dating burnt or heated objects. It is widely used in determining the date of archeological objects  and antique such as pottery, porcelain, burnt soil in addition, flint, sedimentary soils.

Optically Stimulated Luminescence Dating

In recent years, Optically Stimulated Luminescence Dating, abbreviated OSL, was developed based on the principle from the TL dating method. Instead of heat, OSL uses an argon ion laser or xenon lamp to excite the stored energy. A more accurate date can be obtained if one compares the results from OSL and TL methods.

Reference:

（1）PhyloTree.org - mtDNA tree Build 14 (5 Apr 2012).

（2）Spencer Wells, “The Journey of Man: A Genetic Odyssey” book，Part 3.

（3）Underhill PA, et. al. “Y chromosome sequence variation and the history of human populations”，2000 Nature    America Inc.

（4）Dorit RL, Akashi H, Gilbert W.  “Absence of polymorphism at the ZFY

       locus on the human Y chromosome.”Science 268:1183–1185 1955.

（5）Bing Su, et. al., Y-Chromosome Evidence for a Northward Migration of Modern Humans into Eastern Asia during the Last Ice Age，American Journal of Human Genetics.1999 Dec.

（6）WANG Chuanchao,YAN Shi,LI Hui , Surnames and the Y Chromosomes, Communication on Contemporary Anthropology Vol. 4 2010.

（7）LianZhen Chai，"C14 dating ─ - the method for prehistoric archaeological dating.", Institute of Archaeology,Chinese Academy of Social Sciences.