填空题
Scientists have discovered evidence of the world’s earliest animals, (36) back 635 million years, before the end of the last ice age. Scientists have found evidence of the world’s earliest multicellular animal life, sponges 408 million years older than the oldest known dinosaur remains, 100 million years older than when scientists thought the first animal life (37)
Earth scientist Gordon Love of the University of California, Riverside (38) the team that made the discovery. He says the 635-million-year-old fossils were found in sedimentary rocks in a (39) in southern Oman and are in the form of steroids, essential biochemicals in the cell membranes of sponges.
"Some of the natural products produced by sponges produce very (40) structures," said Love. "Even when they get (41) for hundreds of millions of years in sediments. Basically when the structures of the molecules get tweaked a little bit, we can still recognize the basic (42) skeleton that alerts us to the fact that these were (43) by ancient sponges."
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He adds that research will now concentrate on whether environmental changes between the two great ice ages caused animal life to flourish. " (45) ______ Did the animals appear as we fell into the glacial period ordid they appear after the glaciation, is really the next question, I think (46) in which they first appeared," he said.