英语听力：冰河绿洲—13

But despite their name, the mighty Everglades did not exist during the ice age. So what did pre-historic Florida look like? There is one place in northern Florida that has revealed more ice age secrets than almost anywhere else, the dark slow-moving waters of the Aucilla River. Here ideal conditions for fossilization created a hidden store of ice age evidence. Unlike in the crystal clear spring waters, these clues were never unveiled for all to see. But the Aucilla has now been studied intensively for more than 20 years.

Along some stretches of the riverbed were massive bones recreated here, perfectly preserved for more than 13,000 years. One of the most significant discoveries was the huge skull of an American mastodon. Mastodons, close relatives of mammoths, were widespread all over North America during the ice age. They grew over three metres tall, the size of Africa elephants today. We know a lot about the mastodons, especially their diet, thanks to the preserved dung they left behind.