60秒科学:Plants Put the Bend in Rivers（在线收听）

Plants Put the Bend in Rivers
Studies in the journals Geology and Earth-Science Reviews reveal that ancient rivers were broad straight sheets of water. Colonization by plants changed the water flow. Adam Hinterthuer reports

What was around the bend in rivers hundreds of millions of years ago? It’s a trick question—because there weren’t any bends. Ancient rivers were typically just wide, sheetlike flows of water. New reports in the journals Geology and Earth-Science Reviews say we can thank the very first landlubbing plants for putting the turn in the river.

Researchers from Dalhousie University examined dozens of sites, from the Channel Islands off France to Death Valley. They say that well before dinosaurs or, really, much of anything roamed the Earth, rivers were just vast expanses of water heeding only gravity and heading straight to sea.

The first vascular plants took advantage of the abundant water, and put down roots. The roots began to hold sediment in place. Thus the riverbank was born and waterways began to get thinner and more defined. The communities of Paleozoic plants congregated at the water’s edge and began to colonize the Earth’s surface.

Over the next 50 million years this co-evolution of flora and flow led to the meandering rivers we know today, and a barren landscape made lush. And, also, the seven-dollar toll to cross the Hudson on the George Washington Bridge.