Afarensis is a 3.5-2.8 million year old hominin from the Kada Hadar member of the Hadar formation in the Middle Awash, Ethiopia. He is approximately 41 inches tall, weighs approximately 60 pounds and has a cranial capacity of a whopping 410 cc (approximately). Afarensis is currently considered to be transitional between apes and humans and displays some traits of both. Since he spends a lot of time on the couch watching monster movies, some observers question whether he is an obligate biped (although no one has observed him climbing a tree). He also has a blog called 
This is cool! The paper concerns a novel method of determining age based on accelerator mass spectrometry analysis of the carbon content of the lens crystallines. It is quite similar in methodology to the use of teeth to determine age.
Like the enamel in teeth, lens crystallines do not turn over:
Lens crystallines are special proteins in the eye lens. Because the epithelial basement membrane (lens capsule) completely encloses the lens, desquamation of aging cells is impossible, and due to the complete absence of blood vessels or transport of metabolites in this area, there is no subsequent remodelling of these fibers, nor removal of degraded lens fibers. Human tissue ultimately derives its 14C content from the atmospheric carbon dioxide. The 14C content of the lens proteins thus reflects the atmospheric content of 14C when the lens crystallines were formed. Precise radiocarbon dating is made possible by comparing the 14C content of the lens crystallines to the so-called bomb pulse, i.e. a plot of the atmospheric 14C content since the Second World War, when there was a significant increase due to nuclear-bomb testing. Since the change in concentration is significant even on a yearly basis this allows very accurate dating.
Like the method for determining age from teeth, this method relies on the decreasing amount of C14 in the atmosphere to determine age. C14 is largely produced in the upper atmosphere via the impact of cosmic rays on nitrogen atoms. Another source of C14 production are the nuclear bomb tests that occurred in the 1950's-1960's. Some estimates indicate that the amount of C14 nearly doubled during that time period, but has been steadily decreasing since then. Essentially, the sample, in this case the eye lens, is processed and run through an AMS and the number of C14 are counted and calibrated against the known concentrations of C14 thus giving an age. To a certain extent, the title of the post is misleading, there is no radiometric dating involved in that the time frames involved are too small for radioactive decay to be relevant. The technique is more similar to stable isotope analysis in that it is the amount of C14 that is important. There are two drawbacks to the method. First, a diet heavy in marine foods could affect the date. Second, since the C14 is being extracted from the lens decomposition becomes an issue. The authors estimate that the lens can be extracted up to three days post-mortem.
Humanities & Social Science
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