The age of the carbonates in martian meteorite ALH84001

The age of secondary carbonate mineralization in the martian meteorite ALH8 4001 was determined to be 3.90 +/- 0.04 billion years by rubidium-strontium (Rb-Sr) dating and 4.04 +/- 0.10 billion years by Lead-Lead (Pb-Pb) dating . The Rb-Sr and Pb-Pb isochrons are defined by Leachates of a mixture of hi gh-graded carbonate (visually estimated as similar to 5 percent). whitlocki te (trace), and orthopyroxene (similar to 95 percent). The carbonate format ion age is contemporaneous with a period in martian history when the surfac e is thought to have had flowing water, but also was undergoing heavy bomba rdment by meteorites. Therefore, this age does not distinguish between aque ous and impact origins for the carbonates.