Every one has heard the story which has gone the rounds of New England, of a strong and beautiful bug which came out of the dry leaf of an old table of apple-tree wood, which had stood in a farmer's kitchen for sixty years, first in Connecticut, and afterward in Massachusetts -- from an egg deposited in the living tree many years earlier still, as appeared by counting the
annual layers beyond it; which was heard gnawing out for several weeks, hatched perchance by the heat of an urn.
A year's worth of snow can be crunched down to form an
annual layer that normally survives hundreds--if not thousands--of years.
However, the differences may be related to the interpretation of the position of the first
annual layer The accessory layers (nonannual), observed between the neonatal line and the end of the GLG of the first year, frequently appear in a very conspicuous manner, especially in the tip of the tooth, and can be easily confused with
annual layers.
Each
annual layer, known as a varve, contains organic evidence of the earth's climate and ocean temperatures for the year it was deposited, Briskin says.
By analyzing every single
annual layer in the kilometres long ice cores, researchers can get detailed information about the climate of the past.
He also "gained the ability to recognize
annual layers in the ice cores we were studying," he explained yesterday.
Near the surface, one meter of snow is equal to a year of accumulation, but at greater depths the
annual layers are compressed to centimeters of ice.
Using a hi-tech X-ray mud core scanner, Dr Henry Lamb, of Aberystwyth's Institute of Geography and Earth Sciences, and post-doctoral researcher Dr Mike Marshall undertook the painstaking work of counting and characterising the
annual layers in the lake's cores, many of which were too fine to be distinguished by the naked eye.
Snow falls atop the ice sheet in
annual layers, so the deeper you drill, the further back in time you go.
The researchers counted
annual layers of overlying glacial sediments and used radiocarbon dating to analyze plant fossils at the lake bottom (the last vestiges of the old tundra).
These signals allow the identification of individual
annual layers which can be counted backwards from the present day (their modern anchor being the snowfall of the year of coring).
Glaciers record the deposition of snow in
annual layers.
