FOOL鈥橲 gold could be the key to finding ancient life on Earth, or even on Mars if it ever existed there.
Most researchers hunt for fossilised bacteria in a kind of sedimentary rock called chert. These rocks are hard enough to last a long time, and thin slices can be transparent, making it easy to see what鈥檚 inside. But both chert and the fossils within it are relatively rare.
Back in 1965, scientists noticed that microbial fossils can also be preserved in pyrite, or fool鈥檚 gold. Flakes of pyrite are found in almost all marine rock. But back in the sixties, the techniques needed to whittle pyrite down to slices thin enough to examine with an electron microscope were so difficult that researchers avoided trying to look for the fossils.
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Now, however, instruments called ion mills can pare down the rock atom by atom, making pyrite the perfect place to go fossil hunting. So J眉rgen Schieber, a geologist from the University of Texas at Arlington, cracked open a handful of random rock samples from his own collection to see how easy it would be. The rocks came from around the world, and spanned from the Archaean to the Jurassic鈥攁bout 3 billion to 150 million years ago.
Five out of the six contained what looked convincingly like fossil microbes inside their pyrite flakes. 鈥淚 was surprised by how common it was,鈥� he says.
John Parkes, a geomicrobiologist from Bristol University, isn鈥檛 convinced that all the traces are actually fossils rather than just crystal grains or side effects of the tools used to pare away the rock. Schieber admits that more work needs to be done to confirm the finds, but he is already convinced there are more fossils in pyrite than in chert. He adds that recent pictures of Mars indicate that rocky outcrops there are layered with mudstone, which should be packed with pyrite, and maybe fossils too (Geology, vol 30, p 531).