PLANET EARTH Caves

These flooded caves in Mexico have remained virtually unchanged for thousands of years. Since the last Ice Age they've become cut off from the outside world. Yet their impact on life on the surface has been huge. 500 years ago they supported one of the world's great civilizations the Maya. Mexico's Yucatan Peninsula（尤卡坦半岛） has no rivers, lakes or streams so the Maya relied on the cenotes（沼穴，这里特指尤卡坦半岛的灰岩坑） - the flooded entrances to the water-filled caves. These flooded shafts are the region's only source of open fresh water.



The cenotes are, in effect, gigantic fresh water wells. Away from the life-giving rays of sunshine one might not expect to find plants. But in the darkness of the cave tunnels roots of giant tropical trees have pushed their way through cracks in the limestone to reach the flooded caverns.



Without this water the Yucatan's forest could not grow so luxuriantly（壮观地）. The Maya knew that their lives depended on this water, but it's only with the help of today's technology that we've come to appreciate the full significance and scale of these flooded passageways. So far, more than 350 miles of underwater galleries in the Yucatan have been mapped, but still nobody yet knows the true extend of this subterranean water（地下水） world. And with good reason.