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Live long and prosper

发布时间:2019-03-07 13:08:02来源:未知点击:

By Jeff Hecht HUGE unicellular organisms entombed in the pyramids of Egypt grew so large because they lived for up to a hundred years, says an Oxford geologist. Layers of the shells called nummulites accumulated in a now-vanished ocean that once separated Africa from Eurasia. The shells formed the limestone used in Egyptian monuments such as the Sphinx. Nummulite fossils were recognised in ancient times; the Greek historian Herodotus thought they were the remains of lentils eaten by Egyptian pyramid-builders. What interests modern-day palaeontologists is the enormous size of the coin-like fossils. The largest modern nummulites are about two millimetres wide, but those that lived 50 million years ago grew up to 16 centimetres across. “They were the dinosaurs of the unicellular world,” says Martin Brasier of the University of Oxford. Brasier and postgraduate student Louise Purton took samples from 1-centimetre nummulites that lived 42.5 to 50 million years ago in England. From annual variations in carbon and oxygen isotope levels they worked out that the British nummulites lived for up to five years (Geology, vol 27, p 711). They estimate that the largest species must have lived for about a hundred years, but have not found samples that are preserved well enough to analyse. Ancient nummulites thrived in a warm and stable climate, says Brasier: “Creatures that develop in very stable conditions build up a lot of biomass, live a long time, and reproduce at exactly the optimal moment.” Later, as the climate changed,