The Earth is currently in an Ice Age, evident by the fact that both northern and southern polar extremes are covered in ice. During this current Ice Age, the glacial period, when glaciers were advancing, occurred during the Pleistocene between 100,000 and 12,000 years ago. Presently, Earth is in an interglacial period of the Ice Age, when glaciers are retreating. The maximum extent of glaciation occurred about 18,000 years ago and it is during this time that the environments of the northern and southern hemispheres were much different than they are today.
Studying Earth's Climatic History
There are many ways that scientists can piece together the climatic history of Earth. If scientists are looking back only a few hundred years, a very complete record of meteorological data can be used. However, if scientists are looking back a few thousand or hundreds of thousand of years, well before humans began to record climate and weather data, scientists must look for clues that are recorded in the stratigraphic history of the Earth. Biological and geological activity leave behind clues in the stratigraphic record, and these clues can be later found and identified for how they fit into the climate puzzle. Scientists refer to this information as "proxy data" for past environments.
These biological and geological proxy data include:
- Glacial ice deposits. Past climate conditions can be recorded in gas bubbles that are trapped in ice deposits. Some of these ice deposits are hundreds of thousands of years old, recording environmental conditions from as far back as 750,000 years ago.
- Fossilized marine fauna and flora. Paleontologists study these fossils for abundance, morphological changes and oxygen isotopic concentrations.
- Marine sediment. Past sea-levels are recorded in the types and geomorphology of marine sediment deposits. Sea-level can be related to the abundance or absence of ice.
- Geological deposits and formations. Glacial activity, lake activity and shoreline activity all leave behind unique deposits in the geologic record that can tell scientists something about the extent of glaciers, glacial lake sizes and sea-level conditions. Even the formation of caves can be related to inland sea activity, telling scientists the seas covered continents.
- Fossilized terrestrial fauna and flora. Like fossilized marine life, terrestrial fossils can give clues about the conditions of life on land.
The Environment During Earth's Maximum Glaciation
To support the advancement of ice away from the poles and towards mid-latitude regions, the temperatures of the Earth must have been much cooler than they are today. Biological and geological proxy data paint a picture of the Earth that was much different 18,000 years ago than it is today.
Some of the clues left behind by the Earth's maximum glaciation are:
- Antarctic ice core data suggests carbon dioxide levels that were about 200 ppm (compared to today's >300 ppm) and temperatures 6 to 8 degrees Celsius lower than today.
- Glacial deposits that extend to the mid-latitudes of the North American and European continents, suggesting that these areas were completely covered by ice.
- Shoreline deposits that extend farther into oceans than today's shorelines, suggesting much lower sea-levels, up to 100 meters, and enlarged coastal plains as much of the Earth's water was locked up into glaciers.
- Fossilized fauna and flora that thrived in wet environments found in today's Southwest and Saharan deserts, suggesting that much cooler and wetter environments existed in these areas.
Although the environment of the Southern hemisphere was also much different, the difference is not as dramatic as in the Northern hemisphere. Antarctic ice sheets extended much farther into the ocean, but did not make it as far as to cover continents in the Southern hemisphere. Soon after this period of maximum glaciation, carbon dioxide levels increased, the Earth warmed and glaciers began to retreat, which continues today and is known as the Holocene period.
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