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  • 地球历史上的气候变化

    A prehistoric scene with a human chasing a mammoth in an icy landscape.
     

    How important was the Pleistocene ice age to human evolution?
    ::冰河冰河时代对于人类进化有多重要?

    Climate  is dynamic; climate has changed through Earth's history. Climate has changed a lot during the time humans have been evolving. As the climate got colder, people learned to hunt more since plants became scarce in the winter. Better hunting required better tools. Better tools helped to spur on the evolution of culture.
    ::气候是动态的; 气候已经随着地球的历史而变化。 在人类进化期间,气候已经发生了许多变化。 随着气候变冷,人们学会了更多的狩猎,因为植物在冬季变得稀缺。更好的狩猎需要更好的工具。更好的工具有助于刺激文化的进化。

    How Earth’s Climate Changes
    ::地球的气候变化如何

    Earth’s climate has changed many times through Earth's history. Over much of Earth’s past, the climate was warmer than it is today. Picture in your mind dinosaurs roaming the land. They're probably doing it in a pretty warm climate ( Figure   )!
    ::地球的气候在地球历史中已经发生了许多变化。 在地球的过去的大部分时间里,气候比今天更温暖。在你的脑海中想象恐龙在这片土地上游荡。他们很可能是在一个非常温暖的气候中这样做的(图 ) 。

    Dinosaurs in a warm prehistoric landscape with trees and mountains.
     
    Dinosaurs thrived during one of the warmest periods in Earth's history.

    Ice ages  also occurred many times in the past. An  ice age  is a period when temperatures are cooler than normal. During an ice age, ice caps cover both poles, and   spread to lower latitudes. Scientists have identified five major ice ages in Earth’s history. How do scientists learn about Earth’s past climates?
    ::过去,冰河时代也曾发生过许多次。 冰河时代是一个温度比正常温度更冷的时期。 在冰河时代,冰盖覆盖两极,并蔓延到低纬度地区。 科学家已经确定了地球历史上五大冰河时代。 科学家如何了解地球过去气候?

    The last major ice age took place in the Pleistocene. This epoch lasted from 2 million to 14,000 years ago. Earth’s   was only 5° C (9° F) cooler than it is today. But glaciers covered much of the  Northern Hemisphere . Below, you can see how far south they went ( Figure   ). Clearly, a small change in temperature can have a big impact on the  planet . Humans lived during this ice age.
    ::上一次主要的冰河时代发生在Pleistocene。 这个时代从200万年到14000年前持续了。 地球比今天更冷,只有5°C(9°F ) 。 但冰川覆盖了北半球的大部分地区。 下面,你可以看到冰川向南走多远(图 ) 。 显然,气温的微小变化会对地球产生很大影响。 人类生活在冰河时代。

    Map showing the extent of Pleistocene glaciers in the Northern Hemisphere.
     
    Pleistocene glaciers covered an enormous land area. Chicago is just one city that couldn't have existed during the Pleistocene.

    Why Climate Changes
    ::为什么气候变化

    Several natural processes may affect Earth’s temperature. They range from  sunspots  to Earth’s wobble.
    ::一些自然过程可能会影响地球的温度,从日落到地球的摇晃。

    • Sunspots  are  storms  on the  . When the number of sunspots is high, the Sun gives off more  energy  than usual. Still, there is little evidence for climate changing along with the sunspot cycle.
      ::太阳点是暴风雨。当太阳点数高时,太阳释放的能量比平常要多。然而,随着太阳点周期的变化,气候变化和日点循环的证据仍然很少。
    • Plate  movements cause continents to drift closer to the poles or the  equator . Ocean currents also shift when continents drift. All these changes can affect Earth’s temperature.
      ::板块运动导致大陆向极或赤道移动。 当大陆漂移时,洋流也会发生变化。 所有这些变化都会影响地球的温度。
    • Plate movements trigger  . Many eruptions release  greenhouse gases , which make the Earth warmer. Some major eruptions have been known to spew so much gas and ash into the air that little sunlight would reach the surface for months, temporarily lowering Earth’s temperature.
      ::板块运动触发。 许多火山爆发释放了温室气体,使地球更暖和。 已知一些大型火山爆发将大量气体和灰尘喷入空气中,几乎没有阳光照射到地表数月,暂时降低了地球的温度。
    • A large   hitting Earth would throw a lot of dust into the air. This could block sunlight and cool the planet.
      ::巨大的撞击地球会把大量的尘埃 投向空气中。这可以阻挡阳光和冷却地球。
    • Earth goes through regular changes in its position relative to the Sun. Its  orbit  changes slightly. Earth also wobbles on its  axis of rotation . The planet also changes its  axial tilt , the angle of its axis of rotation. These changes can affect Earth’s temperature.
      ::地球相对太阳的位置经常发生变化。它的轨道略有变化。地球也在其旋转轴上摇晃。行星也改变其轴倾斜,即旋转轴的角。这些变化会影响地球的温度。

    Summary
     ::摘要

    • Earth's climate has been warmer and colder, but mostly warmer, through Earth history.
      ::地球的气候在地球历史中变暖和变冷,但大多是变暖。
    • Many natural processes change Earth's climate. These include sunspots, plate tectonics, volcanism, asteroid impacts, and Earth's motions.
      ::许多自然过程改变了地球的气候,包括太阳点、板块构造、火山学、小行星撞击和地球运动。
    • The Pleistocene Ice Age lasted from 2 million to 14,000 years ago. Earth’s temperature was only 5° C (9° F) cooler than it is today.
      ::冰河时代从200万年持续到14 000年前。 地球的温度比今天只有5摄氏度(9摄氏度)更冷。

    Review
     ::回顾

    1. How has climate changed in the past 14,000 years?
      ::过去14 000年中,气候是如何变化的?
    1. How can the Sun change Earth's climate?
      ::太阳如何改变地球的气候?
    1. What is an ice age? When was the most recent?
      ::什么是冰河时代?

    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。

     

     

    This video deals with the time period at the end of the Paleozoic, called the Permian, 250,000,000 years ago. At that time there was a great mass extinction. Since it was so long ago, scientists must use many types of evidence to determine its cause.
    ::这段影片讲述了Paleozoic的末期,即25万年前的Permian。当时发生了大规模的灭绝。由于这是很久以前的事,科学家们必须使用许多类型的证据来确定其原因。

    1. What were therapsids? What was their great accomplishment?
      ::什么是草率?他们的伟大成就是什么?
    1. What occurred 250 million years ago?
      ::二亿五千万年前发生了什么?
    1. What natural disaster occurred at around the same time?
      ::大约在同一时间发生什么自然灾害?
    1. How much warming did Peter Ward calculate could have happened as a result of this natural disaster? What evidence did he use for his calculation?
      ::彼得·沃德计算了多少变暖 可能是由于这次自然灾害造成的?他用什么证据来计算?
    1. Did this explain the mass extinction at the end of the Permian? Why or why not?
      ::这是否解释了为什么在波尔米安岛末期大规模灭绝的原因?为什么或为什么不呢?
    1. What happened during the first phase of the extinction?
      ::在灭绝的第一阶段发生了什么?
    1. What happened during the second phase of the extinction?
      ::在灭绝的第二阶段发生了什么?
    1. What happened during the third phase of the extinction?
      ::在灭绝的第三阶段发生了什么?
    1. What increased between the marine extinction and the final land extinction? What caused this?
      ::从海洋灭绝到最终土地灭绝之间,到底增加了多少?是什么原因?
    1. In all, what caused the Earth's temperature to rise by 10 degrees?
      ::总而言之,是什么原因导致地球温度上升了10度?
    1. How long did it take for life to recover? What animals came to dominate the Earth?
      ::生命恢复需要多长时间?什么动物主宰地球?