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
Related Stories
The Orange County Register reports on an ongoing survey of the sea floor around Greenland.
The authors of Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, west Greenland (DOI: 10.1002/2016GL067832) measured "seafloor depths 100–1000 m deeper than in existing charts." They explain that, near Greenland, salty 2.5°C water lies beneath 1°C water with a lesser concentration of salt. Hence glaciers in deep water are likely to melt more, due to contact with warm sea water, than those in shallow water.
Further information:
Oceans Melting Greenland portal
UC Irvine press release
UC Irvine Magazine essay
Related stories:
Scientists: Greenland Ice Sheet is Melting Freakishly Early
Greenland Was Once Ice Free
In Greenland, Another Major Glacier Comes Undone
Vegetarianism Reflected in the Genes
(Score: 2, Disagree) by Anonymous Coward on Thursday December 17 2015, @03:26AM
Because the vikings found it covered in grass when they originally came across it and settled there.
(Score: 4, Informative) by Anonymous Coward on Thursday December 17 2015, @03:32AM
https://en.wikipedia.org/wiki/Greenland#Etymology [wikipedia.org]
(Score: 2) by Thexalon on Thursday December 17 2015, @02:36PM
In other words, the name was one of the earliest recorded instances of false advertising.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by M. Baranczak on Thursday December 17 2015, @03:22PM
(Score: 1, Disagree) by Some call me Tim on Thursday December 17 2015, @04:44AM
Hello, McFly!!! I knew this is Jr. High school in the 70's. Is our education system really this bad?
Questioning science is how you do science!
(Score: 4, Insightful) by DeathMonkey on Thursday December 17 2015, @06:28PM
I knew this is Jr. High school in the 70's. Is our education system really this bad?
Apparently it was in the 70's...
(Score: 0) by Anonymous Coward on Thursday December 17 2015, @03:28AM
The real question is if Iceland was ever green-free.
(Score: 2) by Gaaark on Thursday December 17 2015, @03:00PM
and gluten-free???
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2, Insightful) by Username on Thursday December 17 2015, @04:16AM
So how did they stop the global warming 100,000 years ago? Is it when the Flintstones went from evil dino power to green foot power?
(Score: 3, Funny) by Some call me Tim on Thursday December 17 2015, @04:46AM
You haven't heard? The EPA mandated that catalytic converters had to be installed on all dinosaurs.
Questioning science is how you do science!
(Score: 3, Funny) by davester666 on Thursday December 17 2015, @06:15AM
They killed all the dinosaurs to stop all that methane from entering the atmosphere.
You think cow farts are bad...
(Score: 0) by Anonymous Coward on Thursday December 17 2015, @08:23AM
Same way they protected their electronics from massive solar coronal ejections.
There are several [nature.com] potential [sciencedaily.com] consequences [researchgate.net] that could be disastrous for human civilization, without resulting in the complete eradication of Earth's biosphere.
(Score: 1, Interesting) by khallow on Thursday December 17 2015, @11:29AM
(Score: 1) by Some call me Tim on Thursday December 17 2015, @04:54AM
So they found traces of an old beryllium sphere from the Aluminum Falcon and went from there? Dammit Chewbaka, I thought I told you not to leave beryllium laying around after repairs!
Questioning science is how you do science!
(Score: 4, Interesting) by NoMaster on Thursday December 17 2015, @05:20AM
Well, there's plenty of evidence world-wide for a sudden 3-4 meter rise in sea levels over a 500-1000 year period about 127kya, followed by another quick (500-1000 year) rise of 6m or so about 120kya. As far as I know that's not really disputed by anyone except the total sea-level-rise-denialist crazies, and one of the remaining questions is "was it the ice sheet melting in Greenland, Antarctica, somewhere else, or something else that caused it?".
This suggests it might have been Greenland...
Live free or fuck off and take your naïve Libertarian fantasies with you...
(Score: 2) by zocalo on Thursday December 17 2015, @09:50AM
UNIX? They're not even circumcised! Savages!
(Score: 1, Informative) by Anonymous Coward on Thursday December 17 2015, @05:42PM
That should say decreased albedo, of course.
(Score: 2) by zocalo on Friday December 18 2015, @04:01PM
UNIX? They're not even circumcised! Savages!
(Score: 2) by Runaway1956 on Thursday December 17 2015, @02:54PM
I think that any sudden rise in sea level would reflect global events. With a lot of research, you may or may not pinpoint the bulk of the rise to one or two sources, but the effects would almost have to be global in nature. I can't imagine how you could cause half the ice in the northern hemisphere to melt away, while preventing any ice in the southern hemisphere from melting.
And, of course, I can't stop myself reminding people that way back in 1961, my first grade teacher was offering us information on the ice ages, and taught us that we were in an interglacial period. We KNEW THEN that the earth was going to warm up some more. The question is, how much is it going to warm? Nobody knows - and no one can claim to know for certain that mankind has accelerated that warming.
Nature can be a bitch.
Abortion is the number one killed of children in the United States.
(Score: 1) by WalksOnDirt on Thursday December 17 2015, @04:26PM
It had been slowly cooling for 8,000 years or so. How did we know it was going to start warming?
Oh, yeah, the increasing carbon dioxide in the air.
(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.
Abortion is the number one killed of children in the United States.
(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.