英语听力:探索发现 2012-11-09 美洲大平原 American Serengeti—6(在线收听) |
The site was once a spring-fed pond, full of water. Mammoths were tempted in to drink. But when they tried to climb back out, the banks were steep and slippery. Just like the short-faced bear imprisoned underground, some became trapped. Scavengers would have been attracted by the mammoths' plight. The bones of wolf, coyote, and the short-faced bear have also been recovered from the dried-up sediment. The search for food was probably their death pool,too.
These prairie ponds are like time capsules. And they store another kind of data, showing how the plains have changed across millennia. Each spring, pollen from nearby plants is blown into the water. It sinks and settles layer upon layer on the bottom, building into a data bank of local plant life that we can still read today.
And grass pollens aren’t the only clue still sandwiched in the sediment. There are a wide variety of tree pollens, too, from aspens, spruce and other trees, both coniferous and deciduous. |
原文地址:http://www.tingroom.com/lesson/yytltsfx/2012/244984.html |