Asteroid strikes can preserve ancient plant fragments

BBC : Although asteroid impacts have been known to destroy life on local and global scales, researchers have found that they can also preserve biological samples. When asteroids crash into the ground, they melt the surrounding rock, which can then coat bits of vegetation before cooling and rehardening. Peter Schultz of Brown University and colleagues have found ancient samples of grass preserved in so-called impact glass distributed in sedimentary layers of loess in the Pampas region of Argentina. When they tried to re-create the conditions necessary to trap and preserve the grass, they found that temperature was critical. Below 1500 °C, the grass burned to a crisp; above that, the leaves were conserved. The researchers propose that bubbling occurring along the plants’ edges as water turned to steam may have insulated the plants’ interior. By analyzing the plant remains, the researchers have recovered metal oxides and organic compounds. They think genetic material, such as DNA or RNA, might also be preserved. The discovery could provide a way to search for past life on Mars.