Amazon River Reversed Twice, Study Indicates --WaPo

[Demeter]

http://www.washingtonpost.com/wp-dyn/content/article/2006/10/24/AR2006102401228.html?referrer=email

We humans see a river and assume it has pretty much always been the way it is -- flowing from some highlands ultimately down to the sea. Sure, dams and floods and erosion can change its appearance, but it would take something unthinkable to actually reverse its direction.

Yet new research concludes that one of the world's mightiest rivers, the Amazon, once emptied into the Pacific rather than the Atlantic, as it does now. Sometime around 65 million years ago -- almost yesterday in geological time -- the rise of the Andes blocked the westward flow and sent water back east instead.

The discovery was made by researchers at the University of North Carolina at Chapel Hill, who found 2 billion-year-old samples of the mineral zircon at the center of the Amazon basin -- deposits that could only have come from the now-eroded mountain range to the east called the Purus Arch.

The geologists also concluded that the reversal to an eastward flow was but the latest of a number of direction changes. Eons before, the Purus Arch was pushed up in movements associated with the breaking apart of the South American and African tectonic plates. The rise of that north-south range is what turned the Amazon westward in the first place.

"Although the Amazon seems permanent and unchanging," team member Russell W. Mapes said, "it has actually gone through three different stages of drainage since the mid-Cretaceous, a short period of time geologically speaking" -- about 110 million years. Mapes will present his findings today at the annual meeting of the Geological Society of America. "The surface of the Earth," he said, "is very transient."


-- Marc Kaufman

[Kutjara]

1. So you're saying the Amazon...

...flip flopped and failed to stay the course? Damned liberal river.

[donheld]

2. NO! NO! NO!

God yelled at the river "Back the hell up bitch" and back it went :D

[EST]

4. She did it to be tricky

All that evidence, like dinosaur remains, was put there to confuse us and to point out, through fundy dead enders, that logic, truth and minimum standards have no more than a marginal effect on human alignment.

[acmejack]

3. "Reality has a notorious liberal bias!"

[Igel]

5. Nah, it's stayed the course.

It's still there, isn't it?

[eppur_se_muova]

6. Sometimes a new exit strategy is just what's needed. nt