章节大纲

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  • 第一单元

    Microscopic view of green bacteria, representing early single-celled life forms on Earth.

    What did the first life forms look like?
    ::第一生命形式是什么样子的?

    The first forms of life on Earth were probably smaller and simpler than even these bacteria . The first forms of life had to be simple single-celled organisms . But how did life begin on Earth?
    ::地球上第一种生命形式可能比这些细菌都小,更简单。第一种生命形式必须是简单的单细胞生物。但生命是如何在地球上开始的呢?

    Origin of Life
    ::生命起源

    There is good evidence that life has probably existed on Earth for most of Earth’s history. of blue-green found in Australia are the oldest fossils of life forms on Earth. They are at least 3.5 billion years old ( Figure ).
    ::有良好的证据表明,地球的大部分历史都可能存在生命。 澳大利亚发现的蓝色绿色是地球上生命形式最古老的化石。 它们至少有35亿年的历史(图 ) 。

    Stromatolites in a coastal area, indicative of early life forms on Earth.

    Some of the oldest fossils on Earth were found along the coast of Australia, similar to the area shown here.
    ::地球上一些最古老的化石 在澳大利亚海岸一带被发现 与这里显示的区域相似

    Life from Random Reactions
    ::随机反应生命

    How did life begin? In order to answer this question, scientists need to know what kinds of materials were available at that time. We know that the ingredients for life were present at the beginning of Earth’s history. Scientists believe early Earth did not contain oxygen gas ( had yet to evolve), but did contain other gases, including:
    ::生命是如何开始的?为了回答这个问题,科学家们需要知道当时有什么样的材料。 我们知道生命的成分存在于地球历史的开端。 科学家们相信早期的地球并不含有氧气(尚未进化 ) , 但确实含有其他气体,包括:

    • nitrogen gas,
      ::氮气,
    • carbon dioxide,
      ::二氧化碳,
    • carbon monoxide ,
      ::一氧化碳,
    • water vapor,
      ::水蒸气,
    • hydrogen sulfide.
      ::硫化氢。

    Where did these ingredients come from? Some chemicals were in water and volcanic gases ( Figure ). Other chemicals would have come from meteorites in space. Energy to drive chemical reactions was provided by volcanic eruptions and lightning. Today, we have evidence that life on Earth came from random reactions between chemical compounds, which formed molecules , or groups of atoms bonded together. Small molecules, such as those present in the early atmosphere , can provide the components (including the elements C, H, N, O and S) to make larger molecules. These early molecules further reacted and eventually formed even larger molecules and , such as amino acids (which combine to form proteins), and nucleotides (which form nucleic acids - or DNA). These organic molecules eventually came together in the right combinations to form basic cells . The components that were necessary for the formation of the first cells are still being studied.
    ::这些成分来自哪里?有些化学物质来自水和火山气体(图 ) 。其他化学物质来自空间中的陨石 。推动化学反应的能量来自火山爆发和闪电。今天,我们有证据表明,地球上的生命来自化学化合物之间的随机反应,这些化合物形成分子,或原子的组合。小型分子,如早期大气中的分子,可以提供组成较大分子的成分(包括元素C、H、N、O和S)。这些早期分子进一步反应,最终形成更大的分子,如氨酸(形成蛋白质)和核糖核酸(形成核酸-或DNA)等。这些有机分子最终形成形成形成基本细胞的正确组合。最初细胞形成所需的成分仍在研究中。

    How long did it take to develop the first life forms? As much as 1 billion years. Many scientists still study the origin of the first life forms because there are many questions left unanswered, such as, "Did proteins or nucleic acids develop first?" or "What exactly were early Earth's atmospheric conditions like?" There is a lot of work still left to answer these and similar questions.
    ::开发第一种生命形式需要多长时间? 多达10亿年。 许多科学家仍在研究第一种生命形式的起源, 因为还有许多问题没有回答, 比如“蛋白质或核酸是先开发出来的?” 或“地球早期的大气状况究竟像什么?” 还有大量工作要做来回答这些问题和类似的问题。

    Aerial view of Grand Prismatic Spring, showcasing its colorful thermal waters and surrounding landscape.

    Some clues to the origins of life on Earth come from studying the early life forms that developed in hot springs, such as the Grand Prismatic Spring at Yellowstone National Park. This spring is approximately 250 feet deep and 300 feet wide.
    ::地球生命起源的一些线索来自研究在温泉中形成的早期生命形式,例如黄石公园的Grand Priistical Spring,今年春天的深度约为250英尺,宽度约为300英尺。

    Summary
    ::摘要

    • Life has probably existed on Earth for most of Earth’s history.
      ::地球的大部分历史都可能存在地球上的生命。
    • Life on Earth came from random reactions between chemical compounds, which formed molecules.
      ::地球上的生命来自化学化合物之间的随机反应,化学化合物形成分子。

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    • Thrombolites Differ From Stromatolites at (6:24)
      :伤心6:24) Stromatolites 的异样(6:24)
    1. What are the environmental conditions like in Shark Bay? How does this differ from other oceanic conditions?
      ::鲨鱼湾的环境条件如何?这与其他海洋条件有何不同?
    2. What type of organism do scientists believe was responsible for the increase in oxygen (O 2 ) in the Earth's atmosphere?
      ::科学家认为哪种生物对地球大气层氧气(O2)的增加负有责任?
    3. What types of structures did these organisms build that scientists are studying today? How old are the oldest of these structures?
      ::这些生物建立了哪些类型的结构,科学家们今天正在研究这些结构?这些结构中最古老的几岁?
    4. When did the abundance of stromatolites go into decline? What else happened at this time?
      ::大量的地磁石何时开始衰落?
    5. What are thrombolites? How do they differ from stromatolites?
      ::血栓石是什么?它们与石马石有何不同?

    Review
    ::回顾

    1. How did life on Earth begin?
      ::地球上的生命是怎么开始的?
    2. Describe how the early atmosphere of Earth was different than it is today.
      ::描述地球早期的大气层与今天的大气层有何不同。
    3. List three gases present in the early atmosphere.
      ::列出早期大气中存在的三种气体。
    4. How long did it take to develop the first life forms?
      ::开发第一种生命形式需要多长时间?