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Much of climate history is recorded in four
climate archives: |
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(1)
Sediments |
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(2)
Ice |
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(3)
Corals |
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(4)
Trees |
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How are those records dated? |
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Hoe much of Earth’s history each archive spans? |
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What is the resolution of climate history
yielded by each? |
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Sediments are the major climate archive on Earth
for over 99% of geological time (and on all time scales), primarily as
continuous sequences deposited by water. |
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Rainfall and the runoff it produces erode rocks
exposed on the continents and transport the eroded sediments in streams and
rivers. |
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The sediments are deposited in quieter waters
where layer upon layer of sediments can be laid down in undisturbed
succession. |
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For intervals before the last 170 million years,
all surviving sedimentary records come from continents. |
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Ice cores retrieve climate records extending
back thousands of years in small mountain glaciers to as much as hundreds
of thousands of years in continental sized ice sheets. |
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The antarctic ice sheet has layers that extend
back over 400,000 years. |
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The Greenland ice sheet has layers that extended
back 100,000 years. |
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Trees are climate archives for the interval of
the last few tens and hundreds of years. |
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The outer softwood layers of many kinds of trees
are deposited in millimeter-thick layers that turn into hardwood. |
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These annual layers are best developed in middle
and high latitudes, where seasonal climate changes are larger. |
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Corals form annual bands of CaCO3 that hold
several kinds of geochemical information about climate. |
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Individual corals may live for time spans of
years to tens or hundreds of years. |
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Coral archives are located at tropical and
subtropical latitudes. |
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Notes