章节大纲

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  • 早期大气和海洋

    Volcanic eruption on the left; a comet in the night sky on the right.
     

    What did Earth look like at first?
    ::地球一开始是什么样子的?

    The earliest Earth did not have an  atmosphere  or free  water . The  planet  was far too hot for gases and water to collect. The atmosphere and oceans that we see today evolved over time. The gases came from volcanic eruptions and from  .
    ::最早的地球没有大气层或自由水,地球太热,不能收集气体和水,我们今天看到的大气层和海洋随着时间的演变而变化,气体来自火山爆发和火山爆发。

    Formation of the Atmosphere and Oceans
    ::大气层和海洋的形成

    An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not  stable .
    ::大气层是环绕地球的气体。 早期的地球没有大气层。 条件非常热,气体不稳定。

    Earth's First Atmosphere
    ::地球第一个大气层

    Earth’s first atmosphere was different from the current one. The gases came from two sources.   spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and  water vapor , or water in gas form, were in the first atmosphere ( Figure  ). Take a look at the list of gases. What's missing? The early atmosphere had almost no oxygen.
    ::地球第一个大气与当前不同。 气体来自两个来源。 气体从两个来源流入空气。 彗星从外层空间的冰层中携带。 这些冰层温暖而成为气体。 氮、二氧化碳、氢、水蒸气或气体形式的水在第一个大气中(图 ) 。 看看气体清单。 缺少什么? 早期的大气几乎没有氧气。

    A geothermal area with steam rising from water, surrounded by trees and rocky terrain.
     
    Gases from Earth’s interior came through volcanoes and into the atmosphere.

    The Early Oceans
    ::早期海洋

    Earth’s atmosphere slowly cooled. Once it was cooler, water vapor could condense. It changed back to its liquid form. Liquid water could fall to Earth’s surface as  rain . Over millions of years water collected to form the oceans. Water began to cycle on Earth as water evaporated from the oceans and returned again as rainfall.
    ::地球的大气慢慢冷却。 一旦变冷,水蒸气就会凝结,水流会变回液态。 液体水会随着雨滴落到地球表面。 数以百万计的采集水形成海洋。 水开始在地球循环,水从海洋蒸发,又随着降雨回流。

    Streams  carry dissolved  . These  ions  make the oceans salty. Marine sedimentary   are found that are four billion years old. The first oceans could have formed as early as 4.2 to 4.4 billion years ago!
    ::海洋沉积场被发现已有40亿年的历史。最早的海洋可能早在42至44亿年前就已经形成!

    The Later Atmosphere
    ::后来的大气

    Eventually,  photosynthesis  evolved. The first photosynthetic organisms were probably  cyanobacteria , which began releasing a significant amount of oxygen into the atmosphere about 2.4 billion years ago. Many organisms died off because they could not handle the oxygen. But this development was extremely important for other life. Single-celled  eukaryotes , including algae and other protists, appeared about 2.1 billion years ago.  These eventually gave rise to animals and plants, which could not survive without oxygen.
    ::最终,光合作用演变了。 第一批光合作用生物可能是氰化细菌,它大约在24亿年前开始向大气释放大量氧气。许多生物由于不能处理氧气而死亡。但这一发展对于其他生命来说至关重要。 单细胞的环状藻类和其他原生生物在21亿年前出现。它们最终产生了动物和植物,没有氧气就无法生存。

    Oxygen is needed to make  ozone . Ozone is a  molecule  made of three oxygen atoms. Ozone in the upper atmosphere blocks harmful solar radiation from reaching the surface. Without oxygen, life on Earth would have been very simple.
    ::制造臭氧需要氧气。臭氧是由三个氧原子组成的分子。上层大气中的臭氧将有害太阳辐射屏蔽到表面。没有氧气,地球上的生命就会非常简单。

    Summary
    ::摘要

    • Earth's first atmosphere came from the planet's interior. Gases also came from asteroids and comets from elsewhere in the solar system.
      ::地球第一个大气层来自地球的内部,气体也来自太阳系其他地方的小行星和彗星。
    • There was very little oxygen in the atmosphere until photosynthesis evolved. Oxygen allowed multicellular life to evolve and ozone to form.
      ::在光合作用进化之前,大气中氧气很少,氧允许多细胞生命进化,臭氧形成。
    • The first oceans formed when water rained out of the atmosphere into basins.
      ::当海水从大气中降下 进入盆地时 形成第一个海洋

    Review
    ::回顾

    1. What were the sources of gases in Earth's early atmosphere?
      ::地球早期大气中的气体来源是什么?
    1. Where did oxygen come from? Why is oxygen so important for life on Earth?
      ::为什么氧对地球上的生命如此重要?
    1. How did the first oceans form?
      ::第一大洋是怎样形成的?