SCIENCE MAGAZINE has a busy day today. Appearing in the current issue are two important articles.
The first is a follow-up on Mary Schweitzer’s and coworkers’ work in extracting and analyzing collagen from a T. rex fossil. Sequencing of protein fragments and construction of a phylogenetic tree showed T. rex shared most similarity with birds and crocodilians, as we would expect. However, Pavel Pevzner has some critical but vague comments about the study, and has a paper on the topic coming out soon. It’s unclear what his objections are, but probably they are regarding the methodology and not the conclusions, since Pevzner works in bioinformatics. This is not the first criticism these studies have received. We’ll see what comes of this. Thanks to Bruises Colours for drawing my attention to the Washington Post article.
The second is the successful synchronization of the 40Ar/39Ar and U/Pb dating methods. These had been just slightly disagreeing, probably due to inaccuracies in the ages of standards and a decay rate that is slightly off. This new study calibrates the 40Ar/39Ar method to the astronomical ages of sediments that were deposited in a cyclical pattern (due to climatic effects of the earth’s orbital wobble) and can be dated to within approximately 10,000 years. The result is an agreement of the U/Pb methods and tightening of the uncertainty of 40Ar/39Ar dating to about 0.25%, from approximately 2.5%.
This means that the timing of certain events has been pushed slightly farther into the past, so the K-T impact took place about 66 million years ago instead of 65.5 million years ago. This modification correlates well with other data. Other extinction events will likewise be shifted slightly.
Organ, C. L.; Schweitzer, M. H.; Zheng, W.; Freimark, L. M.; Cantley, L. C.; Asara, J. M. “Molecular Phylogenetics of Mastodon and Tyrannosaurus rex.” Science 2008, 320, 449. doi:10.1126/science.1154284
Kuiper, K. F.; Deino, A.; Hilgen, F. J., Krijgsman, W.; Renne, P. R.; Wijbrans, J. R. “Synchronizing Rock Clocks of Earth History.” Science 2008, 320, 500-504. doi:10.1126/science.1154339