2005 Annual Science Report
University of California, Los Angeles Reporting | JUL 2004 – JUN 2005
Earth's Early Environment and Life
Field work was conducted in the 3.5-3.2 Ga Barberton greenstone belt, South Africa for three weeks, July 2004. Several meteorite impact spherule layers were examined in place, and samples collected for future analytical studies.
Materials from two of five possible meteorite impact layers were processed to examine heavy minerals looking for nickel spinels and separate zircons. Spinels found only had compositions consistent with terrestrial volcanic sources. Zircons were isolated, mounted and polished, and examined and photographed in transmitted light, backscatter, and CL in preparation for U-Pb isotopic microanalysis at the USGS-SHRIMP laboratory at Stanford. One sample yielded an age near 3225 Ma and likely represents a new impact layer in the Archean. The second sample contained mostly discordant zircons and the age obtained only allows us to confirm that the impact layer in this new terrain represents one of the three (now four?) large impacts at circa 3225-3255 Ma.
A paper on impact layer “S3” from the Barberton greenstone belt is in preparation.
Six impact samples previously collected are being processed for zircons. One is for the attempt to corroborate the 3225 Ma age of the youngest Barberton impact. The others are to confirm the ages of S2 and S3 across several regional faults.
PROJECT INVESTIGATORS:Gary Byerly
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere
Effects of extraterrestrial events upon the biosphere