It's easy to get overwhelmed when you start looking into geology.
Both the size scale and the time scale are so immense that it's hard to wrap your brain around them. Huge forces at work, that have been at work for billions of years -- and will continue to work for another billion. Makes me feel awfully... insignificant.
The topic comes up because of three recent bits of research into just how powerful geological processes can be. In the first, scientists were studying a crater field in Wyoming that dates to the Permian Period, around 280 million years ago (28 million years, give or take, before the biggest mass extinction the Earth has ever experienced). The craters are between ten and seventy meters in diameter, and there are several dozen of them, all dating from right around the same time. The thought was that they were created when an asteroid exploded in the upper atmosphere, raining debris of various sizes on the impact site.
The recent research, though, shows that what happened was even more dramatic."Many of the craters are clustered in groups and are aligned along rays," said Thomas Kenkmann of the University of Freiburg, who led the project. "Furthermore, several craters are elliptical, allowing the reconstruction of the incoming paths of the impactors. The reconstructed trajectories have a radial pattern. The trajectories indicate a single source and show that the craters were formed by ejected blocks from a large primary crater."