91色情片

PhD student Bradd Witt wants to learn
about the changes to vegetation in Australia since widespread grazing by sheep
started about 150 years ago. He has chosen an unusual way to obtain his data.
Witt, from the Research School of Earth Sciences at the Australian National
University, is studying the neatly preserved layers of sheep droppings under
shearing sheds. By analysing the quantity of different carbon isotopes in the
layers, Witt says that he can work out the amount of grass in a sheep鈥檚 diet
compared with the amount of shrubbery or other plant matter. The age of the
droppings can be determined by the depth of the layer under the shed. Witt has
been able to establish when grass species were overcome by shrubs and bushes. 鈥淚
don鈥檛 talk too much about my work at parties,鈥� Witt says.