The document discusses how ice cores can provide information about past climates and atmospheres. Snow that accumulates over time compacts into ice sheets, trapping air bubbles that contain samples of ancient atmospheres. Scientists can determine the age of ice layers using dendrochronology techniques similar to dating tree rings. Ice cores drilled from Antarctica and Greenland provide a record of atmospheric carbon dioxide levels over 800,000 years, showing that pre-industrial CO2 ranged from 180 to 280 ppm, whereas modern CO2 levels have risen above 401 ppm.

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2. Sorge’s Law steadily accumulating snow will reach a certain final
density in the form of ice as it compacts under the weight of new
snow.
Density of Ice Pure ice has a density of 917 kg/m3. Compacting
snow becomes ice around 830 kg/m3 because some air spaces close
off and become air bubbles, limiting density.

3. Dendrochronology Like a tree’s growth rings, accumulating ice
have visible seasonal layers which allow scientists to calculate how
old the ice is at greater depth.
Ice Forensics The air pockets which limit the density of glacial ice
contain a frozen record of the earth’s atmosphere at the time in which
they were created.

4. Antarctic Ice Sheet Approximately 61% of all earth’s fresh
water is held in it. It is reported that on average the ice sheet is
2,000 meters thick, and its maximum thickness is 4,770 meters.
Deep Ice Sheet Coring Drill The University of Wisconsin built
this machine, which is capable of cutting and extracting 12 cm-
wide ice cores from 4,000 meters of depth, allowing scientists to
peer back 800,000 years into the earth’s atmospheric record.

5. From the ice cores, scientists have
determined that atmospheric CO2
levels for the 800,000 years preceding
the Industrial Revolution ranged
between 180 – 280 ppm.
Atmospheric CO2
As of July 2015, the level was 401 ppm.