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Lions and Tigers and Bears, Oh my!

Studies from the New Mexico Geochronology Research Laboratory

Actually, its bacteria and elephants and monkeys and humans, oh my! Geochronology (the determination of a rock's age) has a wide variety of applications; one of which is placing absolute age constraints on evolution. The New Mexico Geochronology Research Laboratory mainly focuses on projects in New Mexico and the Southwestern USA. However, in a role that fulfills its broader commitment to the scientific community, projects are undertaken from throughout the world. Recent collaborations with geologists, archeologists, and biologists have lead to exciting advances in our understanding of

  1. Mammal evolution in South America, including a refinement of when North American and South American critters began walking the present land bridge between the continents,
  2. When humans arrived in Java, Indonesia, and
  3. Confirmation that bacteria have lived in salt crystals found near the WIPP site in New Mexico for more than 200 million years

Publication and/or submission of these findings are being recognized in internationally acclaimed journals such as the Proceedings of the National Academy of Sciences, Nature, Science, and Geology.

Increased understanding of mammal evolution in South America stems from dating volcanic ash that can blanket the landscape following an eruption. The ash accumulation represents an instantaneous point in time that can be used to determine or bracket the age of fossils. Such studies in Patagonia with collaborators at Duke University show that mammals, which have placentas (rather than marsupials, which have pouches) were around nearly 40 million years ago, which is 20 million years earlier than previously thought. Additionally, tooth structure evolution indicates a drying climate that correlates to Antarctic glaciation at this time. A similar study in conjunction with the Los Angeles Natural History Museum uses the occurrences of volcanic ashes and elephant fossils in eastern Peru to determine that the land bridge now connecting North and South America formed as long ago as 9.5 million years. This is significant because it was previously thought that North American elephants did not have access to South America until about 2 million years ago.

The chronology of Homo erectus evolution has been extensively studied in East Africa. However, little age information is available for the rich Homo erectus fossil assemblage in Java, Indonesia. We have determined that hominid fossils (sampled by anthropologists at the University of Iowa) in Java are at least 1.6 million years old, which indicates dispersal out of Africa (not the movie) by this time. Dating a section of sediment that contains bones ranging from 1.6 to 1.0 million years ago shows that evolutionary trends in Java were very similar to Africa.

Oh the stories you could tell if you were 200 million years old and still living! A bacteria colony has been successfully extracted and cultured from brine trapped in salt crystals near Carlsbad, NM by a group of biologists at West Chester University in Pennsylvania. The age of the salt has been confirmed by dating at both the Berkeley Geochronology Center and the New Mexico Geochronology Research Laboratory to be at least 200 Ma, and perhaps as old as 250 Ma. The age of this living colony extends by more than 100 million years the previously documented length of time that bacteria can survive within geological samples.