Everyone knows that dinosaurs are extinct, and most people have some idea about how it might have occurred. But the exact ...

the period that closes the Proterozoic era. If they were wiped out by an extinction event, changes in sea level or lowered oxygen levels are likely to blame. But if, as most scientists think ...

From oldest to youngest, they are the Hadeon, Archean, Proterozoic ... to fill the available ecological niches created by a mass extinction event that took place at the end of the Paleozoic ...