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  • General

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  • 生命的灭绝和辐射

    A colorful, fluffy monster with one eye, wings, and a bow, looking surprised.
     

    What is next for life on Earth?
    ::地球生命的下一个是什么?

    Life is dynamic!  Species  begin,  populations  grow, species die out, new species are born. Extinction is an important part of this. If organisms never went  extinct , there wouldn't be any  habitats  available for new ones to arise. What could be next?
    ::生命是动态的! 物种开始, 种群增长, 物种死亡, 新的物种诞生。 灭绝是其中的一个重要部分。 如果生物从未灭绝, 那么新的生物就不会出现任何栖息地。 接下来会是什么?

    Extinction
    ::灭绝

    Most of the species that have lived have also gone extinct. There are two ways to go extinct. The most obvious way is to die out completely. The other way a species goes extinct is if it evolves into a different species. Extinction is a normal part of Earth's history. Most of the organisms that have lived have gone extinct.
    ::大多数物种也灭绝了。有两种方法可以消灭。最明显的方法是彻底灭绝。另一种方法是灭绝,如果物种演变成不同的物种。灭绝是地球历史的正常部分。大多数生物已经灭绝。

    Sometimes large numbers of species go extinct in a short amount of time. This is a  mass extinction . The causes of different mass extinctions are different: collisions with   or  , massive volcanic eruptions, or rapidly changing  climate  are all possible causes of some of these disasters ( Figure ).
    ::有时,大量物种在短短的时间内灭绝,这是大规模灭绝,造成大规模灭绝的原因不同:与这些灾害发生碰撞或爆发大规模火山爆发,或气候迅速变化,都是造成其中一些灾害的可能原因(图)。

    Fossil skeleton of a Tyrannosaurus rex displayed in a museum setting.
     
    An extinct Tyrannosaurus rex. This fossil resembles a living organism.

    Adaptive Radiation
    ::适应性辐射

    After a mass extinction, many habitats are no longer inhabited by organisms because they have gone extinct. With new habitats available, some species will adapt to the new environments. Evolutionary processes act rapidly during these times. Many new species evolve to fill those available habitats. The process in which many new species evolve in a short period of time to fill available niches is called  adaptive radiation . At the end of this period of rapid evolution, the life forms do not look much like the ones that were around before the mass extinction. One example came after the extinction of the dinosaurs. Mammals underwent adaptive radiation and became the dominant life form. Although they lived in the habitats the dinosaurs had lived in, they didn't look much like the dinosaurs.
    ::在大规模灭绝之后,许多生境不再被生物所居住,因为它们已经灭绝了。有了新的生境,一些物种将适应新的环境。进化过程在这些时候迅速发生。许多新的物种演变以填补现有的生境。许多新的物种在短短的时间内演变以填补现有位置的过程称为适应性辐射。在这个迅速演变的时期结束时,生命形式看起来不像大规模灭绝之前的物种。恐龙灭绝之后就出现了一个例子。哺乳动物经历了适应性辐射,并成为了主要的生命形式。虽然它们生活在恐龙所居住的生境中,但它们看起来不像恐龙。

    Summary
    ::摘要

    • Species go extinct when all of the individuals die out or evolve into a different species.
      ::当所有人死亡或演变成不同的物种时,物种就会灭绝。
    • Many species go extinct at roughly the same time during a mass extinction.
      ::许多物种在大规模灭绝期间大约同时灭绝。
    • New habitats become available and species evolve to fill them so that biodiversity increases during adaptive radiation.
      ::有了新的生境,物种逐渐演变,以填充这些生境,从而使生物多样性在适应性辐射期间增加。

    Review
    ::回顾

    1. Why is extinction considered a normal part of Earth's history?
      ::为什么灭绝被视为地球历史的正常部分?
    1. What are some of the possible causes of mass extinctions?
      ::大规模灭绝的一些可能原因是什么?
    1. Why do many new species evolve after a mass extinction?
      ::为什么在大规模灭绝后,许多新物种会演变?