Sunnyvale and Del Mar skulls from California and their age

I was reading about the Del Mar remains that were discovered in 1926 on the California coastline and which were dated by Jeffrey L. Bada at 47,000 years old (Bada, J. L., and Helfman, P. M. 1975, Amino Acid Racemization Dating of Fossil Bones. World Archaeology 7 : 160–183.) as shown below (blue box):

They were doing groundbreaking work with a technique that Bada had developed: "amino acid racemization" or AAR for short.

AAR measures the ratio of right-handed amino acids or (D) amino-acids to the left-handed ones or (L) amino-acids, and uses it to determine the age of a biological sample.

All apha-amino acids except glycine come in two isomers, that are identical except that one bends polarized light to the right (hence the right-hand part of the nam), and the other type bends it to the left.

Proteins are made up exclusively of (L) amino acids. And the moment a living being dies, its (L) amino acids start to degrade by a process called "racemization", and become (D) amino acids. There are many amino acids in our bodies, and scientists use one, aspartic acid because it has a relatively quick racemization speed.

As you can see in the table above, older specimens have (D) amino acids and less (L) amino acids, so the ratio D⁄L is higher than in younger specimens.

Bada calibrated his method against a radiocarbon dated specimen (Laguna Skull) and then extrapolated the dates shown in the last column.

Of course, it was a controversial claim, Del Mar skull at 47 ky and the Sunnyvale skull with 70 ky, were far too old for orthodox scholars.

The novel technique was scrutinized and torn apart, other methods (Uranium and Thorium) used on the samples, which gave a much later date, almost one order of magnitude -ten times less- than Bada's data.

To justify Bada, we must admit that despite his claims that "The effects which other physical factors (pH, humidity, leaching) have on racemization rates are discussed. Because of the close correlation between temperatures calculated from in situ racemization rates (under diverse environmental conditions) and actual mean annual temperatures at various sites throughout the world, we conclude that factors other than temperature have very small effects on the reaction rate.", there are many factors that affect racemization.

Bada pointed out in 1984 that radiocarbon dates and AAR didn't seem to correlate in American specimens, while in other parts of the world, the correlation was very good.

Apparently the cause of this discrepancy was the degree of preservation of protein (and therefore amino acids) in the bones (see Stafford, 1990.), meaning that the same bone can give a Holocene or recent dating or a Pleistocene or older date!

So we could argue that the age of Del Mar and Sunnyvale bones might (barely) be 48,000 and 70,000 years old, but then we have the issue of the uranium (U) and thorium (Th) dates (Bischoff, 1981), which gave ages of 11,000 and 8,300 years BP respectively for those remains.

Bones can uptake these elements (U and Th) from the environment which can alter the actual age of the specimens, and (Millard, 1996): "are liable to underestimate the true age by at least one-third."

This would make them younger than they really are...

So the age remains an open question -maybe.

Sunnyvale girl skull

But what drew my attention when I was reading about this subject was the photo of the skull of the "Sunnyvale girl" in New Scientist's edition of Jul. 14, 1983 is shown below:

Sunnyvale skull (left) and 4,000 year old Indian skull (right). New Scientist

That skull is really big! I tried to find other photos, but I wasn't able to. But I found a description of her in this paper (Amino Acid dating and early and early man in the New World, a rebuttal, 1981, Bert A. Gerow, page 9):

"The Sunnyvale individual is a female, judged to have been about twentyfive to thirty years of age at the time of death. Morphologically, she is fully modern, with a well developed chin, thin cranial walls, canine fossae, short face, and sub-quadratic orbits. The lateral incisors exhibit "shoveling" on the lingual side. The latter is a common Amerindian physical trait shared with populations of East Asia. "

One source (Biological and Chronometric Applications of Amino Acid Racemization Reactions, Patricia Masters Helfman, 1976, Biology, Univ. of California, pp. 67) says that it was Gerow who found the "Sunnyvale girl" in 1972, but he does not mention this date in the paper cited further up.

Perhaps some photos of the skull would shed some light on the matter of its size. But if I am not mistaken, these bones were reburied in accordance with the US law back in 1996.

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