Ancient Snapshot (image) Brown University Caption The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. Some of that glass preserves bits of ancient plant material. Credit Brown University Usage Restrictions with credit Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.