Ian
priscilla 1Understanding Ancient Climates
August 13th 2010 03:12
Since about 1850 accurate records of the temperature and climate on planet earth have been kept, with coverage improving over time.
Before this time various proxies must be used to estimate climate conditions. These include tree rings, coral growth, ice cores, ocean and lake sediments, cave deposits, fossils, borehole temperatures, and glacier length records.
Proxies are of course less accurate than direct measurements, but they still tell an interesting and important tale about the history of our planet.
To illustrate, Discover Magazine put together this intriguing article about the keys science can use to decipher ancient climates. Read the full article here.
A study this March of clamshells taken from Iceland found that the levels of oxygen isotopes in the shell layers varied depending on the temperature of the water in which they formed. By slicing tiny layers for analysis, the team found that it could determine temperature variation down to weeks, not just years.
You learn in grade school that each ring in a tree represents a year. But there's more information hidden away in these concentric rings. The thickness of a ring shows how much the tree grew during that year. If scientists know what temperature and moisture level make the tree happy, they can use the thickness to gauge what the climate was like that year.
In the 1960s, scientists began extracting ice cores from Greenland and Antarctica. These frozen columns can compress hundreds of thousands of years into their vertical reach.
Like the clamshells, ice cores tell scientists about the temperature record through their chemical composition, particularly the oxygen isotopes--ice with less heavy oxygen (made heavy by additional neutrons) indicates cooler temperatures. But ice cores can do so much more. The thickness of layers reveals how much snow accumulated in a year. If there's a large different in snow for the same year between one ice core and another, that can indicate which way the wind was blowing. And tiny air bubbles trapped in the ice can allow scientists to see what gases were present in the ancient atmosphere.
Pollen may seem like ephemeral dust when it's aloft on the breeze, but those grains can have surprising staying power in the environment. After plants spread theirs far and wide it can be preserved in lakebeds or fossilized in soil. When scientists take a sediment core, they sometimes find that pollen from different species dominates in different eras. And since plants thrive best under particular temperatures and conditions, researchers can use the pollen mix to determine the climate of an era.
Sediment cores, like ice cores, are vertical columns taken from the ground to extract paleoclimate data.
Before this time various proxies must be used to estimate climate conditions. These include tree rings, coral growth, ice cores, ocean and lake sediments, cave deposits, fossils, borehole temperatures, and glacier length records.
Proxies are of course less accurate than direct measurements, but they still tell an interesting and important tale about the history of our planet.
To illustrate, Discover Magazine put together this intriguing article about the keys science can use to decipher ancient climates. Read the full article here.
Clam Shells
Tree Rings
Ice Cores
Like the clamshells, ice cores tell scientists about the temperature record through their chemical composition, particularly the oxygen isotopes--ice with less heavy oxygen (made heavy by additional neutrons) indicates cooler temperatures. But ice cores can do so much more. The thickness of layers reveals how much snow accumulated in a year. If there's a large different in snow for the same year between one ice core and another, that can indicate which way the wind was blowing. And tiny air bubbles trapped in the ice can allow scientists to see what gases were present in the ancient atmosphere.
Pollen
Sediment Cores
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