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Using data from a 3053-meter-long core of ice and bedrock collected from the center of the island in 1993, Schaefer's team has found valuable clues to what the period held. In particular, the 1.55 meters of bedrock at the core's base revealed much about the island's history of glaciation, Schaefer says, in atoms that chronicle exposure to the elements. Earth's surface is constantly bombarded by cosmic rays, high energy particles streaming into Earth from space. They collide with atoms in Earth's atmosphere as well as in the uppermost centimeters of its rocks, producing new particles. Some of those particles have a particularly useful set of properties: They don't naturally occur in the rocks, and they are radioactive. Thus, they can act as a sort of clock, marking time since the rocks were last ice free and exposed to the atmosphere.
Schaefer and his colleagues measured the abundance of two cosmogenic isotopes, aluminum-26 and beryllium-10, in grains of the mineral quartz that they found within the bedrock. Each isotope is produced at a different rate by cosmic rays and has a different half-life. Once the rocks are no longer exposed to the atmosphere—for example, buried by ice—the ratio of 26Al to 10Be in the rocks changes because of their differing half-lives. Schaefer and his team found that the ratio in the bedrock was simply too low for the site to have remained buried continuously over the last 1.25 million years—suggesting that it had been exposed and ice free at least once during that time.
Schaefer says he is certain the findings show that Greenland was ice free at one point
(Score: 4, Insightful) by Runaway1956 on Thursday December 17 2015, @04:55PM
Say WHAT?!?!?!?!?! What EVER made you believe that the earth had been cooling for 8000 years? Really - PLEASE - post a citation to something that would make anyone believe that. Something somewhat credible, at least, please don't just post some anecdote from some fool who can't even spell "science".
http://www.longrangeweather.com/global_temperatures.htm [longrangeweather.com]
The pretty chart at the bottom of that page does not seem to indicate any "slowly cooling", or, as I read that phrase, "gradual cooling". Rather, it seems to show almost rhythmic fluctuations in climate. Up and down and up and down. I'll grant that the dips seemed to be getting deeper - but we would need to put that chart up against a similar chart for the past 50,000 years to say whether that was an ongoing trend, or - as I say - it's just more or less random short term fluctuations.
In point of fact, the ice receded from as far south as Washington D.C. only about 12,000 years ago, indicating that the long term trend was toward warming, all along.
http://www.livescience.com/40311-pleistocene-epoch.html [livescience.com]
If, as you say, the earth had been cooling for the past 8000 years, that would have meant that the ice that receded from Ontario, New York, Pennsylvania, West Virginia, Maryland, and the District of Columbia would have just turned itself back around, and started moving south again.
(Score: 2, Insightful) by WalksOnDirt on Friday December 18 2015, @12:50AM
As stated on Wikipedia [wikipedia.org], the "Holocene Climatic Optimum was generally warmer than the 20th century".
The accompanying chart [wikipedia.org] shows there has been over 0.5 K of cooling over that last 8,000 years.