History
This rock is theorized to be one of the oldest pieces of the solar system, proposed to have crystallized from molten rock 4.091 billion years ago. Based on chemical analyses, it is thought to have originated on Mars from a period when liquid water — a requirement for the presence of life — probably existed at the now barren planet's surface.
In September 2005, Vicky Hamilton of the University of Hawaii at Manoa presented an analysis of the origin of ALH 84001 using data from the Mars Global Surveyor and Mars Odyssey spacecraft orbiting Mars. According to the analysis, Eos Chasma in the Valles Marineris canyon appears to be the source of the meteorite. The analysis was not conclusive, in part because it was limited to areas of Mars not obscured by dust.
The theory holds that ALH 84001 was shocked and broken by one or more meteorite impacts on the surface of Mars some 3.9 to 4.0 billion years ago, but remained on the planet. It was later blasted off from the surface in a separate impact about 15 million years ago and impacted Earth roughly 13,000 years ago. These dates were established by a variety of radiometric dating techniques, including samarium-neodymium (Sm-Nd), rubidium-strontium (Rb-Sr), potassium-argon (K-Ar), and carbon-14.
It is hypothesized that ALH 84001 originated from a time period during which liquid water may have existed on Mars. Other meteorites that have potential biological markings have generated less interest because they do not originate from a "wet" Mars. ALH 84001 is the only meteorite collected from such a time period.
In October 2011 it was reported that isotopic analysis indicated that the carbonates in ALH 84001 were precipitated at a temperature of 18°C with water and carbon dioxide from the Martian atmosphere. The carbonate carbon and oxygen isotope ratios imply deposition of the carbonates from a gradually evaporating subsurface water body, probably a shallow aquifer meters or tens of meters below the surface.
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