How old is the Murchison Meteorite?

On September 28, 1969 a fireball exploded over Murchison, Australia scattering over 200 pounds of meteoritic material over a 5 square mile area. Collected samples indicated it was a 'Cc2-type' meteor; a Carbonaceous chrondrite, meaning it was rich in carbon compounds. A careful assay of pieces of this meteorite showed it contained traces of 25 out of 20 possible amino acids found in living cells; all were equally left and right-handed which means that no known organic, living process could have formed them. It was dated by Cyril Ponnaperuma and his colleagues at Ames Research Center, and found to be 4.5 billion years old, making it the oldest known remnant of the pre-Earth solar system environment. More recent dating sets its age at nearly 4.95 billion years; nearly 500 million years older than the age of the Earth!

A recent painstaking study of the contents of the available pieces uncovered 720 silicon carbide dust grains embedded in the meteorite, and these seem to fall within several well-defined isotopic and chemical families. In an article in the Astrophysical Journal for 1994, vol. 430, page 870, the investigators led by P. Hoppe propose that these different families indicate separate stellar origins for the dust grains in very old stars on the so-called Asymptotic Giant Branch , and in Wolf-Rayet stars. We know that the interstellar medium is rich in dust grains from thousands of different astronomical sources spread over billions of years, so it is perhaps no wonder that our own solar nebula was contaminated by dust grains from many different sources over time. To find so many separate signatures in a single 200 pound meteorite is exciting!

Copyright 1997 Dr. Sten Odenwald
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