Could meteorite impacts on Earth have provided a habitat for early life? That’s the question being raised by a new study, which reports the first possible identification of fossil microbial traces from within an impact crater. The researchers were looking at rocks from the Ries crater (inset) of southern Germany, a 24-kilometer-wide depression formed about 14.6 million years ago by a meteorite crashing into Earth with the force of 1.8 million Hiroshima bombs. The energy of impacts that create such craters can be high enough to melt rock; these melts cool rapidly, forming impact glass—a smooth, dark rock, similar to its volcanic cousin, obsidian—which contains various microscopic structures and crystals. Among the structures in the Ries glasses are peculiar curved and tubular features, about one-millionth to three-millionths of a meter in diameter. While previously thought to be simply unusual types of crystals, the team’s study revealed that the tubules (pictured) may be biological in origin , they reported online last week in Geology. Unlike microcrystals, for example, the tubules have complex forms—often observed abruptly changing direction to avoid intersecting each other, in a manner consistent with tunneling microbial behavior—and contain organic molecules associated with biological activity; the Ries tubules are also similar to fossil traces of microbes found in volcanic glass. Given that the tubules seem to be associated with fractures and water-cooled margins within the rocks, the researchers propose that hydrothermal activity—the local circulation of heated water, common after impacts—could have allowed microbial colonization of the glass from the surrounding environment. With the origin of life on Earth believed to have coincided with a period of increased impact flux, the idea that meteorite-formed glass might provide a prevalent, viable habitat for microbes could have a significant “impact” on our understanding of how early life developed.
ScienceShot: Meteorite Impacts Could Have Fostered Life on Early Earth