干货分享：托福考试阅读长难句精编21

>>2019年托福考试：干货分享：托福考试阅读长难句精编21

>>托福100分核心课程

1. Off and on throughout the Cretaceous (the last period of the Mesozoic era, during which dinosaurs flourished), large shallow seas covered extensive areas of the continents.

2. Data from diverse sources, including geochemical evidence preserved in seafloor sediments, indicate that the Late Cretaceous climate was milder than today’s.

3. It’s hard to understand why they would not be affected, whereas dinosaurs were left too crippled to cope, especially if, as some scientists believe, dinosaurs were warm-blooded.

4. In view of these facts, scientists hypothesized that a single large asteroid, about 10 to 15 kilometers across, collided with Earth, and the resulting fallout created the boundary clay.

5. These flow features are extensive systems ―sometimes hundreds of kilometers in total length ―of interconnecting, twisting channels that seem to merge into larger, wider channels.

6. A 2003 Mars Global Surveyor image shows what mission specialists think may be a delta―a fan-shaped network of channels and sediments where a river once flowed into a larger body of water, in this case a lake filling a crater in the southern highlands.

7. The Hellas Basin, which measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers below the basin’s rim, is another candidate for an ancient Martian sea.

8. Furthermore, Mars Global Surveyor data released in 2003 seem to indicate that the Martian surface contains too few carbonate rock layers ―layers containing compounds of carbon and oxygen ―that should have been formed in abundance in an ancient ocean.

9. Aside from some small-scale gullies (channels) found since2000, which are inconclusive, astronomers have no direct evidence for liquid water anywhere on the surface of Mars today, and the amount of water vapor in the Martian atmosphere is tiny.

10. It had been assumed that the ice extended westward from the Alaskan/Canadian mountains to the very edge of the continental shelf, the flat, submerged part of the continent that extend into the ocean.

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