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  • 我们的家园星球

    The most basic measurements of the Earth are its size, mass, and density. The ancient Greeks knew that the Earth had a when Aristotle observed the circular shadow of the Earth during a lunar eclipse.    obtained  a first measurement of the radius of the Earth that was within 20% of the value that we can measure today.   Once the radius of the Earth ( R ⊕ )  is known, think about what else can be done!  For example, the distance and the radius of the moon  can be estimated too, by measuring the angular radius ( α )  of Earth during a lunar eclipse (  below).
    ::地球最基本的测量量是其大小、质量和密度。古希腊人知道,亚里士多德在月蚀期间观察地球圆形阴影时,地球曾观测过地球的圆形阴影。 第一次测量了地球半径,该半径在我们今天能够测量值的20%之内。 一旦知道地球的半径( R), 想想还能做什么! 例如, 通过测量月蚀期间的地球角半径( α) , 月球的距离和半径也可以被估计出来 。

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    Once the radius of the Earth is known, it can be used as a measuring stick. During a lunar eclipse the angular size, alpha, can be measured. Using trigonometry, the distance to the moon and the physical radius of the moon can now be derived.
    ::一旦地球半径为人所知,它就可用作测量棒。在月球日蚀时,可以测量角的大小,阿尔法。使用三角测量法,现在可以测出月球的距离和月球的物理半径。

    It is possible that ancient Greeks might have also calculated the density of rocks, about 3   g / c m 3 . Then, assuming a constant density, they could have estimated the mass for the Earth.  This would have been off by a factor of about two  since the interior of the Earth is compressed and has a higher density than surface rocks. These kind of  calculations are often called "order of magnitude" estimates , and factor of two is a great start when nothing is known before.  With density ( ρ )   and radius ( R ) ,  it is easy to calculate the mass  ( M )  of a spherical body:
    ::古希腊人可能也计算了岩石的密度,约为3克/立方厘米。 然后,假设恒定密度,他们本可以估计地球的质量。由于地球内部压缩,密度高于地表岩石,这本可以减少大约两个系数。这些计算通常被称为“数量级”估计,而当以前一无所知时,2系数是一个很大的开端。如果具有密度( ff) 和 半径( R) , 很容易计算球体的质量( M ):

    ρ = M V = M 4 3 π R 3  
    ::MV=M43R3

    By the early 18th century (and with the benefit of insights from Isaac Newton about the laws of gravity) Henry Cavendish had “weighed the Earth” in his lab by cleverly measuring the acceleration of gravity.   Cavendish calculated a bulk density for the Earth of 5.48   g   c m − 3 , very close to the current value of   5.515   g   c m − 3 .  
    ::到18世纪初,亨利·卡文迪什(Henry Cavendish)通过巧妙地测量重力加速度,在他的实验室中“接近地球 ” 。 卡文迪什计算出地球的体积密度为5.48克厘米-3,非常接近当前值5.515克cm-3。

       Order of Magnitude estimates
    ::磁级估计值

    The ancient Greeks are a great role model for  those who  have a hard time believing that the radius, mass, and density of the Earth or the distance to the moon  can be determined with basic high-school mathematics. Undaunted and armed with a basic understanding of elementary mathematics, they devised simple experiments that gave surprisingly accurate estimates.  Before you decide that something is unknowable, pause and think about whether there is a way to make a reasonable estimate, even within a factor of 10 (an "order of magnitude). This will make you a powerful problem - solver in science, business, and life.
    ::对于那些难以相信地球的半径、质量和密度或与月球的距离可以用基础高中数学来确定的人来说,古希腊人是一个伟大的榜样。他们无所畏惧,对基本数学有基本了解,设计了简单的实验,给出了令人惊讶的准确估计。在你们决定某件事是不可知的之前,先停下来思考是否有合理估计的方法,甚至10倍之内(“数量级 ” ) 。 这将使你们成为科学、商业和生命中一个强大的问题解答者。

    Earth’s interior
    ::地球的内部

    We can estimate whether the Earth is hollow, is uniform in density, or contains a higher density core by measuring a physical property called the moment of inertia. Based on this measurement, we know that the Earth has a dense core but the Moon does not.
    ::我们可以通过测量一个称为惯性时刻的物理属性来估计地球是空的、密度一致的,还是含有一个更高的密度核心。 基于这一测量,我们知道地球有一个稠密的核心,但月球却没有。

    Almost everything else we know about the interior of the Earth comes from seismic waves. Seismic waves carry the energy from events like earthquakes or volcanic eruptions. Seismic waves compress the elastic interior of the Earth like sound waves compress the air. The speed of seismic waves depends on the depth and density of medium. The fastest moving P-waves compress material in the direction that they travel. They are the first to arrive at seismic stations and travel through the core of the Earth. Sheering S-waves are slower and do not propagate through liquid material; they are blocked by the liquid core of the Earth. Slower still, R-waves ripple along the surface of the Earth. They arrive last at the seismic stations but have the potential to do the most damage.  A   visualization of seismic activity from the 2013 Pakistan earthquake (video below.... wait for it!) recorded at seismic stations in the U.S., shows the arrival of P- and S-waves and the more damaging up-down motion from surface waves. 
    ::我们所知道的几乎所有关于地球内地的其他东西都来自地震波。地震波从地震或火山爆发等事件中传来能量。地震波压缩地球的弹性内部,如声波压缩空气。地震波的速度取决于中度的深度和密度。P波压缩材料的移动速度最快。它们首先到达地震台站,穿过地球核心。闪烁的S波较慢,不通过液体材料传播;它们被地球的液体核心阻塞。慢速的是,R波波在地球表面的波纹波纹。它们最后到达地震台站,但有可能造成最大的破坏。2013年巴基斯坦地震的地震活动(下面的视频......等待它!)在美国地震站记录到的地震活动(下面的视频......等待它!),显示P波和S波的到来得更快,地波的上向下运动破坏力更大。

    Seismic waves reveal the bulk density structure of the Earth, as depicted in the   below. The core is about half the radius of the Earth and is comprised of an inner core that is about the size of the moon,  surrounded by a molten iron core. The  thick rocky mantle wraps around the core and extends for the other half of the Earth radius. The outer shell is a thin crust of low density rock called the lithosphere. 
    ::地震波揭示了地球的散积密度结构,如下文所述。核心大约是地球半径的一半,由一个与月球大小相近的内核组成,环绕着一个熔铁核心。厚厚的岩石外壳环绕着核心,延伸至地球半径的另一半。外壳是低密度岩石的薄壳,称为岩层。

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    The interior of the Earth contains a double core and is mostly iron and nickel. The inner core is solid and is surrounded by a molten iron layer. The rest of the interior is a low density rocky mantle. The lithosphere is the thin top crust of light rock.
    ::内地有双层岩心,大部分是铁和镍,内地是固体的,四周是熔化铁层,内地是低密度的岩层,岩层是光岩的薄顶壳。

    Some information about the chemical composition of the mantle comes from surface rocks, especially volcanic rock. The mantle is primarily made up of magnesium, iron, silicon, and oxygen. The layered structure of the Earth is a result of differentiation - a process where heavy elements sink into the core. Chemically, the core is believe to be made up primarily of iron, with some nickel and light elements  like sulfur that dissolve easily in these  molten metals. The inner core is solid because it is under so much pressure. 
    ::有关地壳化学成分的一些信息来自地表岩石,特别是火山岩。地壳主要由镁、铁、硅和氧组成。地球的层层结构是分化过程的结果——重元素沉入核心的过程。化学上,核心据信主要由铁组成,有些镍和轻质元素,如硫,很容易在这些熔化金属中溶解。内核是固体的,因为它承受了巨大的压力。

    If you could put the Earth into a giant blender and re-mix  everything,  you would have an Earth-mass blob  that is chemically similar to meteorites  in the asteroid belt. This is because the objects in the asteroid belt are planetary building blocks that were left behind, not swept up into a planet. During the formation process, the  accretion  of these objects to form the Earth  delivered  a tremendous amount of energy that would have melted the  interior core and mantle and triggered the settling of heavy elements. The friction of material falling toward the core delivered another dose of heat - a positive feedback that hastened the differentiation and layering of the Earth. A final source of internal energy that heats the Earth is radioactive decay of heavy elements. About  half of the heat that exists in the interior of the Earth is left over from collisions during formation of the planet.  The rest of the internal heat that exists today comes from radioactive decay.
    ::如果能把地球变成一个巨型搅拌器,并重新组合所有的东西, 你会有一个与小行星带中的陨石化学上类似的地球质量块状体。 这是因为小行星带中的天体是被遗留下来的行星积块, 而不是被冲入行星。 在形成过程中, 这些天体的积积分形成地球, 产生巨大的能量, 将内核和地壳融化, 并触发重元素的沉积。 物质向核心的摩擦又带来了一剂热量—— 一种积极的回馈, 加速了地球的分化和分层。 给地球取暖的最后内在能量来源是重元素的放射性衰变。 地球内部存在的热大约一半是地球形成过程中的碰撞所留下的。 今天存在的内部热的其余部分来自放射性衰变。

    A global magnetic field 
    ::一个全球磁场

    The core of the Earth has a temperature similar to the surface of the Sun.  The   molten   iron core has a turbulent fluid motion that generates electrical currents and spawns a global magnetic field that extends  thousands of miles above the surface of the planet. This magnetic field plays an important role in protecting the atmosphere  by deflecting charged particles that make up the solar wind (  below).   
    ::地球核心的温度与太阳表面的温度相似。熔化的铁核心有动荡的流体运动,产生电流,产生全球磁场,在地球表面上方数千英里。这个磁场通过转移构成太阳风(以下)的带电粒子,在保护大气层方面发挥了重要作用。

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    The invisible global magnetic force field of the Earth protects the upper atmosphere from charged particles that are released during solar flares.
    ::地球的无形全球磁力场保护上层大气不受太阳耀斑期间释放的带电颗粒的影响。

    Conducting currents in the liquid iron core tend to align, forming a dipole (N-S) magnetic field.  However, there is some chaotic randomness in the fluid flows that can twist the currents. When this reaches a critical threshold, the magnetic field of the Earth will reverse. Today the north geographic pole of the Earth is a south magnetic pole but that pole wanders and has weakened by about 15% over the past 200 years.  There is evidence in the geologic record from magnetic minerals that many magnetic pole reversals have occurred in the past and some scientists believe that the . Earth's magnetic field Life has existed on our planet for billions of years, and no correlation has been found between mass extinctions and magnetic pole reversals. The risk to life during a magnetic pole reversal may be modest, but the risk to power grids that modern humans depend upon will be more substantial. 
    ::液态铁芯中的流体流势趋于一致,形成一个极地磁场。 然而,流体流中有一些混乱的随机性,可以扭曲流体。 当它到达临界临界点时,地球磁场就会逆转。 今天,地球的北极是一个南极,但这一极在过去200年中徘徊,并被削弱约15%。 磁质矿物的地质记录显示,过去曾发生过许多磁极逆转,一些科学家相信,地球的磁场生命已经存在了数十亿年,在大规模灭绝和磁极逆转之间没有发现任何关联。磁极逆转期间的生命风险可能不大,但现代人类所依赖的电网风险将更大。

    Plate Tectonics
    ::热点构造构造

    An important property of Earth is that it has plate tectonics. While Venus and Mars are likely to have mantle convection, Earth is the only planet in our solar system known to have plate tectonics. Geological evidence suggests that plate tectonics began operating on the Earth  about 3.8 Gya.  The upper rocky layer of the Earth is divided  into about twelve major tectonic plates that float on top of the convecting mantle. The distribution of  these plates affect global climate because continental crust has a higher albedo than ocean water.   Continental crust was thought to have a maximum extent between 1.6 - 2.7 Gya, causing ice ages and high rates for burial of organic material in the early and late Proterozoic. 
    ::地球的一个重要属性是拥有板块构造学。 虽然金星和火星可能具有地壳对流,但地球是我们太阳系中唯一已知有板块构造学的行星。地质证据表明,板块构造学开始在地球运行大约3.8Gya。地球的上岩层被分为大约12个主要构造板块,这些板块漂浮在交汇层上方。这些板块的分布影响全球气候,因为大陆地壳的反射率高于海洋水。据认为,大陆地壳的最大范围在1.6至2.7Gya之间,导致早期和末期的冰龄和有机材料掩埋率高。

    Plate tectonics provide a mechanism for circulating material between the surface of the planet and Earth's interior. Subduction zones form at boundaries where one edge of an approaching plate moves under another. These  recycling zones   are   critical for life on our planet. They are part of a negative feedback loop that stabilizes our climate  thanks to chemical interactions between surface rocks and the atmosphere.   Rain  removes carbon dioxide from the atmosphere and stores it as calcium carbonate in surface rocks through a weathering process. Carbon-enriched rocks are then transported into the deep mantle along the  subduction zones,  removing excess CO 2 from the atmosphere.  The flow of material goes the other way as well; some elements are transported from the mantle to the surface of the planet. 
    ::热板构造为地球表面与地球内部之间的材料循环提供了一种机制。 潜入区位于接近板块的边缘在另一边缘移动的边界处形成, 这些回收区对我们星球上的生命至关重要。 这些回收区是负面反馈循环的一部分, 由于地表岩石和大气之间的化学相互作用, 从而稳定了我们的气候。 雨水从大气中清除二氧化碳, 并通过天气过程储存二氧化碳作为地表岩石中的碳酸钙。 碳浓缩岩随后被运入沉入沉入地的深层, 从大气中清除多余的二氧化碳。 材料的流向另一个方向流动; 一些元素从地壳迁移到地球表面。

     

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    Look at these images of the four rocky planets in our solar system. What makes Earth the only habitable - and inhabited - planet?
    ::看看这些关于太阳系中四个岩石行星的图像。是什么使地球成为唯一可居住和有人居住的星球?

    Earth's Atmosphere
    ::地球大气层

    Reflect upon the image in  above that compares Mercury, Venus, Earth and Mars. What are the properties of Earth that were fundamental to the emergence of life?   Life requires an inventory of chemicals for self-assembly. Life requires energy to carry out metabolic processes. And life - as we know it - requires water.   The veneer of oceans of water is one important attribute that is unique to the Earth. Water should be a ubiquitous molecule throughout the universe. However, Mercury and Venus are too close to the Sun. Any water that those planets might have had in the past has been lost.  The surface of Mars suggests that it had a water-rich past, but Mars is small and would not have been able maintain a gravitational hold on it’s atmosphere.
    ::以上图像的反射与水星、金星、地球和火星相比。地球的特性对于生命的出现至关重要。生命需要一份化学物质清单来进行自我组装。生命需要能源来进行代谢过程。生命需要水。我们知道,生命需要水。水的特性是地球独有的重要属性之一。水应该是整个宇宙中无处不在的分子。然而,水星和金星太接近太阳了。这些行星过去可能拥有的任何水都已经丢失了。火星表面表明,它有丰富的过去水,但火星很小,无法维持大气层的引力。

    Earth Oceans
    ::地球海洋

    One distinguishing characteristic of Earth is the oceans of water. The oceans on Earth are relatively shallow with an average depth of about 7 km.  Water also cycles through the upper crust of the Earth (about 20% relative to the volume of water in the oceans). And the deep interior may contain several oceans of water. 
    ::地球的一个显著特征是水的海洋,地球上的海洋相对浅,平均深度约为7公里,水也通过地球的上层地壳循环(相对于海洋的水量约为20%),而内地深处可能包含若干水的海洋。

    Earths oceans are thought to be so critical for the emergence of life on Earth that a motto at NASA is "Follow the water."  Where did our oceans come from? The planetesimals  that would have formed Earth should have been water-depleted as they were baked by the energy of the Sun.  But, we know that the planet formation is more complex,  leaving the possibility that  water-rich pebbles were streaming in from the outer solar system and accreting on inner planets. 
    ::据认为,地球海洋对于地球生命的出现是如此重要,以至于美国航天局的座右铭是“跟随水。”我们的海洋从何而来?形成地球的行星的动物本应该因太阳的能量而枯竭。但是,我们知道,地球的形成更为复杂,留下一个可能性,即水量丰富的石块从外太阳系流进,并聚集在内行星上。

    Ask a geologist and most will say that the oceans were outgassed from the Earth mantle. Ask an astronomer and many will suggest that the delivery of water was an afterthought to planet formation.  Comets have been proposed as a possible source of Earth's oceans.  In the early solar system, collisions of comets with the surface of the Earth would have been common enough to deliver several oceans of water. An important clue is the fraction of deuterium (hydrogen with a neutron) to hydrogen - the "D/H" ratio. The value in Earth's oceans is similar to the D/H measured in meteorites. However,  the D/H ratio measured in comets is smaller that terrestrial or meteoritic values and this seems to argue against comets as the source for Earth's oceans.  A better source for water with the correct D/H ratio would be asteroids beyond 2 times the Earth-Sun distance. The origin of Earth's oceans remains a mystery for now. 
    ::问一个地质学家, 多数人会说, 海洋是从地球表面排出气体的。 问一个天文学家, 许多人会说, 水的输送是地球形成的一个事后想法。 彗星被提议为地球海洋的可能来源。 在早期太阳系, 彗星与地球表面的碰撞会非常普遍, 足以输送出若干海洋。 一个重要的线索是当子( 含中子的氢)到氢( “ D/ H” ) 的比例。 地球海洋的价值与在陨石中测得的D/ H 值相似。 然而, 彗星测得的D/ H 比率较小, 与地球或气象值相比, 这似乎反对彗星作为地球海洋的来源。 使用正确的 D/ H 比率的更好的水源将是地球- 太阳距离的两倍以外的小行星。 目前, 地球海洋的起源仍然是个谜。

    The rise of oxygen
    ::氧气的上升

    The Earth is also unique in harboring an oxygen-rich atmosphere, but there are two key lines of evidence showing that it wasn’t always this way. Oxygen is the third most abundant element in the universe. It is an aggressive element that is chemically reactive with other atoms or molecules. Free oxygen would have destroyed nascent organic molecules, so the fact that prebiotic molecules survived and life exists today  implies that the oxygen levels were very low on early Earth. 
    ::地球在保护富氧大气方面也是独一无二的,但有两条关键的证据线表明它并非始终如此。 氧是宇宙中第三大最丰富的元素。 这是一个与其他原子或分子进行化学反应的具有攻击性的元素。 自由氧会摧毁新生的有机分子,因此,生物前分子生存和生命存在的事实意味着早期地球的氧水平非常低。

    The second line of evidence comes from the geologic record. Radiometric techniques are very good at dating rocks on the surface of the Earth and the oldest rocks contain minerals that reveal the chemical constituents of the early atmosphere. We know that there was some  carbon dioxide in the atmosphere because rocky outcroppings that date back 3 Gya contain carbonates that form when carbon dioxide reacts with silicate rocks. Various iron oxides are also found; however, these would only formed if there was a less than a 1% trace of oxygen in the atmosphere.
    ::第二行证据来自地质记录。辐射测量技术非常适合与地球表面的岩石进行约会,而最古老的岩石含有揭示早期大气化学成分的矿物。我们知道大气中存在一些二氧化碳,因为早在3 Gya 的岩石生长间隔期,含有二氧化碳与硅酸盐岩石发生反应时形成的碳酸盐。还发现了各种氧化铁;然而,只有在大气中氧量不到1%时,这些物质才会形成。

    The bulk of the early Earth atmosphere probably consisted of inert neon and nitrogen. The abundance of primordial neon is higher than nitrogen, yet nitrogen atoms in our atmosphere today outnumber neon by 60,000 to 1. The Earth seems to have lost it’s endowment of neon and one theory is that the entire “first atmosphere” of the Earth was blown away during the Late Heavy Bombardment, the time when the surface of the Earth was battered by swarms of meteorites. Later, the atmosphere could have been replenished by volcanic activity, which would have been more frequent when the Earth mantle was hotter.   Volcanoes spew out gases (a process called “outgassing”) that consist of sulphur, nitrogen, carbon dioxide and almost no neon, methane, ammonia or oxygen.
    ::早期地球大气大部分可能由惰性电线和氮组成。 原始奈子的丰度比氮高,然而今天,我们大气中的氮原子数量却超过奈子60,000到1。 地球似乎失去了其天线的特质。 一种理论是,地球的整个“第一大气层”在深重轰炸期间被吹走,当时地球表面被大量陨石撞击。 后来,大气层本可以通过火山活动得到补充,而火山活动在地壳变热时会更加频繁。 火山喷出由硫磺、氮、二氧化碳和几乎没有纳子、甲烷、氨或氧组成的气体(一个叫做“排气过程 ” ) 。

    The first traces of oxygen appeared when ultraviolet radiation from the Sun dissociated water  molecules. The lighter hydrogen was able to escape while heavier oxygen was gravitationally bound to the planet and interacted with iron sediments. This process dehydrated the surfaces of Venus and Mars.  On the surface of Venus, oxygen coupled with carbon to form a C O 2 -rich atmosphere and that greenhouse gas resulted in a runaway warming of the planet that further accelerated the evaporation and dissociation of water molecules. On Mars, the remaining tenuous atmosphere is also made up of carbon dioxide. In his book "Oxygen,"  Nick Lane posits that it was life itself that saved Earth from loss of ocean waters. 
    ::当太阳的紫外线辐射分解水分子时,出现了最初的氧气痕迹。较轻的氢能逃脱,而较重的氧气则与地球引力相连并与铁沉积相互作用。这一过程脱水了金星和火星的表面。在金星表面,氧与碳一起形成二氧化碳含量丰富的大气,温室气体导致地球迅速变暖,进一步加速了水分子的蒸发和分解。在火星上,剩下的脆弱的大气也由二氧化碳组成。尼克·蓝恩在他的书《氧气》中认为,生命本身使地球免于海洋水的流失。

    In the same way that the history of Earth’s atmosphere is written into the geologic record, the evolution of life is written into the genetic record.  The first appearance of life dates back to  between  3 - 4 Gya - shortly after the end of the Late Heavy Bombardment. These first microorganisms, called archea, were anaerobic; they thrived in the absence of oxygen, probably deep in the oceans near thermal vents where chemical gradients could be used as an energy source.  Oxygen would have been poisonous for these anaerobic microbes. But natural selection is a power driver of evolutionary change and around 2.7 Gya, a mutation in the genetic code of anaerobes in the upper layer of the oceans selected for a hardy new organism called cyanobacteria. The remarkable adaptation of cyanobacteria was that they could use energy from the Sun to carry out metabolic processes through oxygenic photosynthesis.  The cyanobacteria took up free CO 2  and began releasing oxygen. This new evolutionary pathway was so efficient that there was an explosion in the population of cyanobacteria and they  drove anaerobic microbes deep into the oceans and began to change the atmospheric composition on Earth.
    ::地球大气层的历史被写进地质记录,生命的进进进也被写进地球记录。生命的进化过程也以同样的方式写进地球记录。生命的首次出现可以追溯到3-4Gya之间的3-4Gya,时间在已故重轰炸结束后不久的3-4Gya之间。生命的首次出现可以追溯到3-4Gya之间。这些最初的微生物,称为Archea,是厌氧;在缺乏氧的情况下,这些微生物,称为Archea,是无厌氧的;它们可能生长在海洋深处,在缺乏氧的海洋中,很可能在热喷口附近,其中化学梯度可以用作一种能源源。对于这些厌氧的微生物微生物来说,它本会有毒。但是自然选择是进化变化的动力动力动力动力动力动力动力动力动力动力动力,在27Gya周围,即生命的首次出现生命的出现。在海洋上层的顶层麻醉动物的基因组的基因组的突变变,即为一种硬性的新生物新生物体,即氰球菌菌菌,它们利用太阳的能量来利用太阳光光光光光光光光光共进行代代进程。它们可以利用太阳的能量来进行代代代代代代代代代代代代代代代代代代代代代代代代代代代代代进过程。这个新进新演变变的宇宙空间变化,开始了大气和驱动。它们。它们。它们。它们的一个新进化过程十分之之之之在大气大气大气变化的宇宙中,在大气组成和动力在大气变化中开始了一种驱动中,开始,开始了一种动力,在大气中开始了一种动力,在大气中,在大气中开始,在大气中开始,在大气中开始,在大气中开始,在大气中开始了一种动力。 的动力的动力。 ,在大气中开始了。

    The evidence for this increase in atmospheric oxygen is also recorded in the geologic record. About 2.5 Gya, the isotopic ratio of sulfur changed, indicating that oxygen levels were starting to rise, and iron minerals showed evidence of increasing oxidation (“rusting”). The production of oxygen by cyanobacteria began to outpace the uptake by reactants in the crust of the Earth and free oxygen began to climb above the initial levels (less than 1%) in the Earth atmosphere. Free oxygen stops the loss of water because as dissociation occurs, oxygen atoms snap up the released hydrogen before it can escape. With todays levels of free oxygen (21%), a mere 3 million tons of water is lost each year. At this rate, only 1% of the ocean’s water would be lost in 4.5 billion years. We can thank cyanobacteria, which still thrive on our planet today, for producing the oxygen that we breath and for saving our oceans of water. 
    ::在地质记录中也记录了大气氧增加的证据。 大约2.5Gya,硫的同位素比变化了,表明氧水平开始上升,而铁矿显示有证据表明氧化增加(“侵吞 ” ) 。 氰球菌的氧产量开始超过地球地壳反应器吸收速度,而自由氧开始超过地球大气初始水平(不到1% ) 。 自由氧停止了水的流失,因为分解发生时,氧原子在释放氢之前就将释放了。 如今,自由氧水平(21 % ) , 仅仅300万吨水每年损失。 以这个速度计算,45亿年中只有1 % 的海洋水会损失。 我们可以感谢今天仍在地球上繁荣的氰球菌,因为它生产了我们呼吸的氧气,并保存了我们的水的海洋。