THE FALLOUT from atomic weapons has led to an unexpected biological
discovery. 快猫短视频s have used the radiocarbon dating signal provided by the
first atomic explosions in 1945 to show that what were thought to be annual
growth rings in the shells of Antarctic brachiopods are in fact laid down in a
cycle averaging almost two years.
Lloyd Peck of the British Antarctic Survey in Cambridge and Thomas Brey of
the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven,
Germany, studied brachiopods collected from the Weddell Sea. Brachiopods, or
lamp shells, are evolutionary leftovers from Palaeozoic times, over 250 million
years ago, when they were the dominant shellfish. Today, they have largely been
replaced by clams but still survive in great numbers in some marine habitats,
including the cold waters of the Southern Ocean.
Peck and Brey began to suspect that there was something strange about the
brachiopods鈥� growth when they measured the shells of some of the animals, then
came back and measured them two years later. Their results suggested that the
creatures were growing much more slowly than the 鈥渁nnual鈥� growth rings
suggested.
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The researchers then turned to radiocarbon dating. The first atom bomb tests
provide a precise dating signal, as they released into the atmosphere
significant quantities of carbon-14鈥攁n isotope that was present only in
tiny amounts until the blasts.
Peck and Brey analysed the position of the sudden upsurge in carbon-14 within
the animals鈥� shells. These results revealed that the rings were not laid down
annually, but rather in a cycle averaging 1.84 years (Nature, vol 380,
p 207). This shows that some brachiopods must live for up to a hundred years,
the researchers say.
Shellfish build their shells in minute daily increments. These usually vary
in size over the year according to lunar cycles and annual fluctuations in water
temperature, resulting in yearly bands like the growth rings on a tree. The
researchers do not yet know why Antarctic brachiopods disobey this rule. An
unknown environmentsl cycle could be the cause, says Peck, 鈥渙r it could reflect
a two-year reproductive cycle鈥�. Reproduction could cause a check on growth, he
explains, which would account for the growth rings.
To investigate this possibility, Peck is now studying the brachiopods鈥�
reproductive biology. He also hopes to repeat the dating experiments with
brachiopods from other parts of the world, to see if they have the same growth
cycle. n