Diamonds Linked to Quick Cooling Eons Ago

NY Times ^ | January 2, 2009 | KENNETH CHANG

[Pharmboy]

University of Oregon
Scientists found microscopic diamonds in the black layer of rock at Murray Springs in Arizona.

At least once in Earth’s history, global warming ended quickly, and scientists have long wondered why.

Now researchers are reporting that the abrupt cooling — which took place about 12,900 years ago, just as the planet was emerging from an ice age — may have been caused by one or more meteors that slammed into North America.

That could explain the extinction of mammoths, saber-tooth tigers and maybe even the first human inhabitants of the Americas, the scientists report in Friday’s issue of the journal Science.

The hypothesis has been regarded skeptically, but its advocates now report perhaps more convincing residue of impact: a thin layer of microscopic diamonds found in rocks across America and in Europe.

“We’re up over 30 sites, as far west as offshore California, as far east as Germany,” said Allen West, a retired geology consultant who is one of the scientists working on the research.

The meteors would have been smaller than the six-mile-wide meteor that struck the Yucatán peninsula 65 million years ago and led to the mass extinctions of the dinosaurs. The killing effects of the hypothesized bombardment 12,900 years ago would have been more subtle.

Climatologists believe that the direct cause of the 1,300-year cold spell, known as the Younger Dryas, was a sudden rush of fresh water from a giant lake in central Canada to the North Atlantic.

Usually a surface current of warm water flows northward in the Atlantic toward Greenland and Europe, then cools and sinks, returning south in the deep ocean. But the fresh water, which is less dense, blocked the sinking of the cold, salty water in the North Atlantic, disrupting the currents.

[Captain Beyond]

bump

[aculeus]

Cool!

[norwaypinesavage]

Eons ago? 13000 years isn’t even roundoff error on the “eon scale”.

[supercat]

How can "less dense" fresh water block the sinking of cold, salty water? Higher density fluids sink relative to other fluids. Is this New York Slimes science, or am I missing something?

If a layer of salt water sits beneath a layer of fresh water, convection will be far less effective than it would be if all water were of uniform salinity. The article's terminology is weird, however, since the salt water wouldn't be stuck on the surface but rather below.

Incidentally, ice is nearly always frozen fresh water; the act of freezing pushes out the salt. This could create variations in salinity, though in most cases natural mixing would prevent them from becoming too significant.

[Lee N. Field]

The big question is: where's the crater(s)?

There's plenty of craters. Earth Impact Database. (Interesting website to peruse. Just FYI, the biggest is the Vredefort ring, in South Africa. 300km across.)

[neverdem]

Thanks for the ping. Happy New Year!

[Pharmboy]

Thanks for the data...good addition to this thread.

[Smedley]

If a layer of salt water sits beneath a layer of fresh water, convection will be far less effective than it would be if all water were of uniform salinity. The article's terminology is weird, however, since the salt water wouldn't be stuck on the surface but rather below.

This I understand, but the scenario is supposedly a layer of fresh water sitting beneath a layer of salt water not allowing the salt water to sink.

This isnt an issue of "terminology" but one of a complete screwup of the description of circumstances.