Under a White Sky

South America, moving northward, gradually caught up with North America, so that by about 3 Myr BP the gap between them was closed, and ocean currents that used to flow westward through that gap were being diverted northward as the Gulf Stream, setting up the pattern of circulating ocean currents that we see today. But the drifting continents were

I kept coming across a similar pattern: events, well-documented in the historic record, that showed how rising and falling precipitation levels contributed to the increase, decrease, and sometimes the complete removal of populations — and ultimately species — from the planet. This was some of the earliest work of its kind.