[meteorite-list] Evidence of Ancient Impact Preserved in Modern Sand

[Ron Baalke]

http://astrobiology.nasa.gov/articles/evidence-of-ancient-impact-preserved-in-modern-sand/

Evidence of Ancient Impact Preserved in Modern Sand
NASA Astrobiology
Daniella Scalice
November 22, 2010

Through NAI's Minority Institution Research Support Program,
scientists at the University of Puerto Rico and their
collaborators have identified a unique record of an ancient
meteorite impact event that is preserved in microstructures in
detrital grains of quartz, zircon, and monazite in the Vaal River,
South Africa. The sand samples were collected from the channel of
the Vaal River near the two billion-year old Vredefort Dome impact
structure, where impact-shocked minerals are known to occur in rocks.

This is the first report that impact shock-deformed minerals
survive the process of uplift, erosion, and sedimentary transport.
The unique mineral shock-deformation was documented by scanning
electron microscopy at the University of Puerto Rico and the
University of Wisconsin. The team's results are published in the
current issue of the GSA Bulletin
<http://gsabulletin.gsapubs.org/content/122/11-12/1968.abstract>.

This result demonstrates that a record of an ancient impact event
can be preserved in sedimentary rocks billions of years after the
impact crater is eroded. This recognition provides a new method to
search for evidence of missing impacts in sedimentary rocks
throughout the geologic time scale. This new insight may lead to
the identification of missing impact events that have been
hypothesized to cause biological mass extinctions, and also impact
events on the early Earth that may have influenced the rise of life.