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Project Progress

We have established that the magnetization in the ALH84001 Martian meteorite dates back to 4.0 billion years, extending our previous constraint that the rock was magnetized at least prior to its ejection from Mars 15 million years ago. Hence, the magnetite and pyrrhotite crystals that preserve this magnetization cannot be of terrestrial origin. This also demonstrates that the planet Mars had a strong magnetic dynamo at least prior to 4 billion years ago, providing both a protection for the atmosphere from solar wind sputtering and pickup, as well as an age constraint on the magnetic lineations in the Southern Highlands. Detailed analysis of the Ar/Ar release history indicates that this rock did not have any significant period of heating even to room temperature for more than about 10,000-100,000 years during this last 4 billion years, providing an exciting constraint on the evolution of Martian surface temperatures. Two papers on this topic are now in press in Earth and Planetary Science Letters (EPSL) (Weiss et al., 2002ab).

Comparison of the nearly complete genomic sequence of two magnetotactic bacteria, strains MS-1 and MC-1, reveal at least 10 clusters of genes that are present in these two organisms that are not present in non-magnetic bacteria, and in which the gene order is preserved. One of these, the MAM cluster, has already been implicated in some aspect of magnetosome formation by transposon mutagenesis studies. If these other clusters are indeed involved in magnetotaxis, their scattered locations around the physical genome argues strongly that magnetotaxis is unlikely to be acquired by lateral gene transfer, and hence may have arisen very close to the root of the bacterial Domain. This is not inconsistent with the presence of putative magnetofossils in the ALH 84001 carbonate globules from Mars.

We have developed a novel hypothesis to explain the unique fluctuations in carbon isotope values that punctuate Cambrian time, particularly the interval of the Early Cambrian evolutionary explosion (evolution’s “Big Bang”). Paleomagnetic evidence suggests that an inertial interchange event occurred, which would rotate large land-based areas from the South Pole to the equator. Episodic release of methane clathrates produced by warming of these areas as they moved into the tropical region would trigger both carbon isotope fluctuations and potentially stimulate biological diversity through greenhouse-induced warming bursts.

Building upon our previous observation that ALH84001 traveled from Mars to Earth without heat sterilization, combined with the possible presence of 4 billion year old bacterial magnetofossils in this meteorite, and by comparing the relative redox potential of the surface environments of Earth and Mars, we have argued that biological evolution may have started on Mars first, and may have been transported to Earth via panspermia (Kirschvink and Weiss, 2002a).