对应考题：2009年1月15日北美托福考试听力第7篇
Once it seemed that the ocean floor was a desert of darkness. As everyone knew, sunlight was what made life possible by fueling photosynthesis, and sunlight can penetrate only the first few hundred yards of the ocean’s great depths. Lower, a few creatures might still eke out a living by scrounging the organic detritus that drifts down from the surface of the sea. But thousands of feet down, in the utter blackness at the ocean’s bottom, there could be practically nothing.
Then, in 1977, underwater explorers discovered that there was in fact something, and quite a lot of it. At mid-ocean ridges, where new ocean floor rises up as molten rock from Earth’s interior, where cold seawater mixes with the rising magma and, heated to 650 degrees, spews back up through chimney-shaped hydrothermal vents, researchers stumbled across bustling ecosystems. Clinging to the sides of the chimneys were thick white mats of bacteria; around them were eight-foot-long stalk-shaped worms, rocking in the water, while eyeless shrimp seethed around the chimneys like maggots. All were thriving on the energy bound up in the vents’ sulfur compounds. The seafloor might still be dark, but now it was known to be dotted with gardens.
In just the past eight years, however, underwater explorers have discovered that this picture is still incomplete: there is light at the bottom of the sea. Hydrothermal vents glow, and while the light is too faint to be perceived by the human eye, that hardly means it is without significance. Physicists maintain that although some of the light may be created by the intense heat, much of it must be attributed to some as-yet- unknown process. Biologists, meanwhile, say there is sufficient light at these vents for photosynthesis to take place. Researchers can’t say yet whether any creatures are actually living off this light, but if they are, they will represent the first known instance of natural photosynthesis without sunlight. The evolutionary implications may run deeper: it’s possible not only that this deep light is fueling photosynthesis now, but that, 3.8 billion years ago, it got the whole process started.
本篇关键词：
Photosynthesis
thousands of feet down
ocean’s bottom
mid-ocean ridges
650 degrees
bustling ecosystems
bound up in
sulfur compounds
light at the bottom of the sea
photosynthesis without sunlight
中文相关知识：
无处不在的细菌：没有阳光就不能进行光合作用，地面生物就无法生存了。但是在2000—3000米深的海底，没有阳光的地方，各种生物又是以什么为食物来维持生命呢？科学家从海底采取的水样中发现了奥妙。原来在水下2500到3000米的海底常有温泉出现，这些温泉喷涌出高达350摄氏度的水流。海底热泉水从地下带上来许多硫酸盐，硫酸盐在高温高压下变成了有臭鸡蛋味的硫化氢，一些以硫化氢为营养的细菌以极快的速度繁衍。细菌通过摄取温泉里丰富的化合物获得能量，它们帮助温泉水把周围变成一片生机勃勃的海底绿洲。小动物就以细菌为食，大动物又以小动物为食，这样就形成了新的食物链。
