The Paleo-ClimateThe average weather over a particular region of the Earth. Climate originates in recurring weather phenomenon that result from specific types of atmospheric circulation. Record
The neat thing about ice is that it is one of nature's best preservatives.
Think about your refrigerator at home... we put food in the fridge and keep it cold because it lasts longer, right? We put food in the freezer and keep it frozen because it lasts way longer.
Now imagine putting something in a place so cold that ice does not melt for 68,000 years! It would practically last forever!
That is basically what has happened in this ice sheet. Every annual layer of ice contains information about the environmental conditions in the year that the snow originally fell. Because it stays cold and doesn't melt, whatever gets stuck in that layer of ice is preserved there for as long as the ice exists.
Take, for example, snow that fell 50,000 years ago.
In order for a snowflake to form, it needed a particle, like a piece of dust, to cling to and crystallize around – a process known as nucleation. That snowflake, with its dust center, falls on top of the then-surface of the ice sheet, along with many others. The snow is light and fluffy at the time, because there are plenty of air pockets in between each snowflake. But as years go by, and more and more snow falls, our 50,000 year-old snowflakes get pushed further and further down, become frozen into ice crystals, and compacted into a thin layer of ice. Some of the air pockets escape, but some get trapped as air bubbles in the ice layer. The dust that the snowflakes nucleated around gets trapped. Anything else that may have been around at the time, like microbes or bacteria that settle on the ice, get trapped as well.
And again, since that ice hasn't melted, everything that is trapped in it is still there, preserved in its original form!
It is due to this process that scientists can now look at a 50,000 year old sample of ice, isolate the air bubbles, dust particles, microbes, and other things in it, and can create a historical record of the environment from that year. They can tell you exactly how much Carbon Dioxide was in the air. They can tell you how much dust was in the air back then. They can tell you if a volcano erupted that year, if there was any microbial growth, and even what the average temperature was for that year, 50,000 years ago. And they can do it very precisely and accurately.
By looking back at samples of ice from every layer of the ice sheet, we can create what's called a Global Paleo-ClimateThe average weather over a particular region of the Earth. Climate originates in recurring weather phenomenon that result from specific types of atmospheric circulation. Record – basically a record of the global climate that goes back hundreds of thousands of years, past the Industrial Revolution, past the advent of agriculture, even past the last ice age – for as old as the ice is!
There is only one problem... how do you get samples of ice that are 50,000 years old?
If they get buried further and further down with each passing year, you can't exactly take a shovel to the ice sheet and dig 2 miles down, can you?
To be continued...
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