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最新推荐文章于 2025-01-12 14:08:54 发布

ujn20161222

最新推荐文章于 2025-01-12 14:08:54 发布

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本文链接：https://blog.youkuaiyun.com/ujn20161222/article/details/87930438

本文探讨了恐龙时代结束后哺乳动物如何从少数小型陆地生物进化为今日我们所知的多样化物种，包括蝙蝠和鲸鱼。文章还详细介绍了支持恐龙灭绝的陨石撞击理论，特别是关于铱元素在6500万年前沉积岩层中异常浓度的发现，这一证据指向了一颗巨大的陨石或小行星撞击地球。

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However, no group or species can maintain its dominance indefinitely, and when, after over 200 million years, the age of dinosaurs came to a dramatic end about 65 million years ago, mammals began to flourish, evolving from relatively few types of small terrestrial animals into the myriad of diverse species, including bats and whales, that we know today.

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Initially, the meteorite theory was based on a single line of evidence. This focused on the chemical composition of ancient rocks. At locations around the globe, geologists had found an unusually high concentration of iridium in the layer of sedimentary rocks that was formed about 65 million years ago. Iridium is an element that is usually uncommon near Earth's surface, but it is abundant in some meteorites. Therefore, Alvarez and his colleagues concluded that it was likely that the iridium in sedimentary rocks deposited at the K-T boundary had originated in a giant meteorite or asteroid.

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