英语听力：自然百科 Dung Heats

The picturesque Western Cape mountain range at the southern tip of Africa lays claim to one of the world's most diverse floral kingdoms. And researchers are scouring the mountains in search of the droppings and urine of a small local inhabitant which could give a glimpse into historic global climate change patterns. The Rock Hyrax, also known as the Rock Rabbit, superficially resembles a guinea pig with small ears and tail. Hyraxes are very social animals and can be commonly found in large groups basking in the sun at the top of the mountain. And, they're a bit of a tourist attraction. The furry little animal is actually a distant relative of the elephant and the manatee. But it is the fossilized excrement of the rock rabbit that has researchers excited. And they're found high in sheltered rock formations, protected from sun and rain. Some of their dung heaps, known as middens, are over 40,000 years old.

Some of these middens are really really old and this one will probably be about 30 to 40 thousand years old. We come across a lot that are, say, 25 thousand years old. And we still need to date this one, but the chances are that it's going to be really old.

Lead researcher Brian Chase says Hyrax dung heaps are especially useful since the animals have a habit of using the same latrine from one generation to the next. The heaps usually consist of hair, excrement, dust, pollen and their characteristic highly viscous urine. When the urine crystallizes, it acts like glue that holds the heaps together. The rock rabbits middens are built up over thousands of years, creating a time capsule carrying vital information on the climate and vegetation of that period in time.

The hyraxes, there is some evidence to suggest that they do use the same latrine preferentially. But these, more often than not, are found under massive overhangs in very protected areas. And the hyraxes are very scared animals, they are often eaten by pretty much everything, so they need to be high off the ground away from leopards and such but protected from eagles. And that's veryconducive to the preservation of the middens because in fact if you rained on this, it will dissolve entirely.

Samples from within the dung heaps can be taken and sent for radio carbon dating. According to the Associated Press, high resolution stable carbon and nitrogen isotope test results reveal that 20,000 years ago, the sea-level in the Western Cape was more than 300 feet below what it is now, around the time when global ice sheets were at their maximum extent. The middens show how the landscape responded to the climate change.

Because of the continuous deposition, you can actually get a picture of how those have changed over timing. You can see how the climate changes through water availability and nitrogen isotopes. And then you can see how the vegetation has changed through the pollen. So you can see the climate dries and, and the grasses start to go away in Namibia and you get more trees and then the succession of various vegetation types.

Southern Africa and other stretches of the continent became colder as the ice age approached, and were very dry. The global climate has cycles and patterns, characterized by a series of lengthy nice ages and shorter, warmer periods such as the current one. And one little furry mountain animal is unknowingly helping the climatologists learn more about those patterns.