Despite the crater's size, it seemed to barely touch life on Earth. In the middle of the Late Devonian Period, one of Earth's largest extinctions appears in the fossil record, but the Alamo impact didn't play a role. It occurred about 3 million years too early to have any connection to the mass die-off. And rocks immediately above the crater hold fossils that are very similar to rocks below the impact, suggesting the impact site was quickly repopulated by the area's sponges, snails, fish and primitive corals.
"Here's a great example of what happens when a meteor or comet hits a marine environment," Tapanila said. "And it doesn't really do a whole lot."
Because half of the Alamo impact crater is buried beneath the earth, there are many remaining mysteries to be solved. "No one knows what the heck made this impact," Tapanila said. No meteorite chunks or extraterrestrial minerals have turned up in the impact-related rocks, so perhaps an icy comet, rather than a meteorite, carved the crater. Geochemical work on the rocks might reveal more details about the source, Tapanila said.