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  • 坎布里安爆炸

    Evolution and Extinction
    ::演变和灭绝

    On geological time scales, time is organized into eons, eras, and periods. There are four main eons subdivided  into different eras. The eras are in turn split into different periods. The current eon, the Phanerozoic Eon (574 Mya through today), is known as "The Age of Life."  The Cambrian Period is the earliest period of the Phanerozoic eon, lasting from 540 to 500 Mya. The events leading up to this period set the stage for an explosion of complex life. Changing atmospheric oxygen concentration  allowed  for more efficient aerobic metabolism  and increasingly complex life forms.
    ::在地质时间尺度上,时间被分为太阳、纪元和时段。有四个主要环子被分为不同的时代。这些时代反过来又被分成不同的时期。当前的环子,即Phanerozoic Eon(574 Mya到今天),被称为“生命时代”。坎布里安时期是Phanerozoic Eon最早的时期,从540到500 Mya。这一时期之前的事件为复杂生命的爆炸创造了条件。改变大气氧浓度,可以提高有氧新陈代谢和日益复杂的生命形式的效率。

     

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    A geological timeline with an emphasis on the Phanerozoic Eon. The oldest events are at the bottom of the figure with the most recent periods at the top. When did the great oxidation event occur relative to this timeline?
    ::以Phanerozoic Eon为主的地质时间段。 最古老的事件位于数字底部, 最近的时期在顶部。 大氧化事件何时发生?

    Precambrian Life
    ::预摄性生命

    T he Proterozoic Eon  began 2.5 billion years ago and set the stage for Phanerozoic life . From the  geologic record, we know that oxygen levels were low  before the Proterozoic. Therefore, microbes from the start of this era would have primarily been anaerobic   chemotrophs, producing energy through chemical pathways.
    ::蛋白质zoic Eon是25亿年前开始的,它为Phanerozoic生命创造了舞台。 从地质记录看,我们知道在蛋白质zoic之前氧气水平很低。 因此,从这个时代开始,微生物主要是厌氧化肥,通过化学途径产生能量。

    The Proterozoic Eon was likely a time of rapid diversification of life. Today, there are  systems of proteins that run checks  during the replication of  DNA to minimize transcription  errors. However, these types of proteins are less common in prokaryotic microbes, which were common during the Proterozoic Era.  A   higher rate of mutations would have accelerated natural selection and a driven greater diversification of organisms. One of those mutations enabled photosynthesis, a more efficient process of respiration, resulting in an explosion of complex multi-cellular organisms that appeared  at the start of the geologic era known as the Cambrian Explosion. 
    ::蛋白质突变很可能是生命迅速多样化的时代。今天,在复制DNA的过程中,有蛋白质系统在进行检查,以尽量减少转录错误;然而,在蛋白质微生物中,这类蛋白质不太常见,而这种微生物在Proterozoic 时代很常见。 突变率的提高本可以加速自然选择和推动生物的更大多样化。 其中一个突变使光合作用,这是一个更有效的呼吸过程,导致在被称为Cambrian爆炸的地质时代之初出现的复杂多细胞生物的爆炸。

    The Cambrian Explosion
    ::坎布里安爆炸

    At the time of the Cambrian explosion, there was an exponential increase in the number and complexity of organisms. Complex  organisms  likely  preferred living   in   the oceans at first, where there was easy mobility and easy access to nutrients. E ven very shallow levels of water provide protection from damaging UV radiation.
    ::在Cambrian爆炸发生时,生物的数量和复杂性呈指数式增长,复杂生物可能首先更喜欢生活在海洋中,因为在那里很容易移动,容易获得养分,即使是非常浅的水,也能够提供保护,避免紫外线辐射的破坏。

    The earliest evidence of complex, land-based life comes from early land plants that begin to appear in the fossil record around 475 Mya. DNA evidence suggests that these plants evolved from algae, a general term for aquatic, photosynthetic organisms. It is a likely transition given that many breeds of algae prefer growing in shallow water to begin with. Algae adapted protections, such as thicker cell wells in order to survive dry spells, that would have been beneficial in the transition from water to land.
    ::陆生生物的最早证据来自早期的陆生植物,这些植物开始出现在475 Mya周围的化石记录中。 DNA证据表明,这些植物从藻类(水生和光合生物的一般术语)演变而来。 考虑到许多种类的藻类倾向于从浅水中生长开始,这很可能是一个转变。 藻类调整了保护方法,如厚细胞井,以生存干燥,这将有利于从水向土地的过渡。

     

     

    Fossils of the earliest land plants. Early land plants were small, simple, and likely remained close to water. Having yet to develop vascular systems, they more likely resembled moss than what we traditionally associate with plants today.
    ::最早的陆地植物的化石。 早期的陆地植物是小的、简单的,并且可能离水很近。 尚未开发血管系统,它们比我们今天传统上与植物的联系更像苔胱。

    With other organisms still constrained to the water, land plants flourished and grew large in size. The lack of competition further allowed  for increasing complexity:  the development of root systems and tubes  to transport water and nutrients throughout the plant. Photosynthesizing land-based plants had abundant energy from the Sun. 
    ::由于其他生物仍然受水的制约,陆地植物蓬勃发展,面积也大增,缺乏竞争进一步增加了复杂性:开发根系统和管子,在整个植物中输送水和养分,光合成的陆基植物拥有来自太阳的丰富能量。

    The Carboniferous Period
    ::碳纤维时代

    Forests  began to cover the lands and dead organic matter began to pile up and decompose among the plants. Millions of years later, this organic matter  would  be compressed into coal,  earning this period  the name "carboniferous," which means "coal carrying'' in Latin.
    ::森林开始覆盖土地,死亡有机物开始在植物中堆积和分解。 数百万年后,这种有机物将被压缩成煤,这段时期的产物名为“碳纤维”,意即拉丁文中的“煤炭载运 ” 。

    The   Carboniferous period   began roughly 360 Mya and  lasted about  60 million years. It was marked by an era of giantism. The fossil record from early in this period is rich in ocean and fresh water organisms.  L and-based organisms  appeared in the middle to later part of the period. The first terrestrial organisms were  supersized insects and amphibians. B y the middle of the Carboniferous period, adult amphibians  were up to 6 meters long and developed the scaly skin typical of lizards by the end of the period. The Arthropleura, which resembles a 2.6-meter long  millipede, proliferated during the late Carboniferous period and remains the largest-known land invertebrate ever discovered.
    ::碳纤维时代开始于大约360万迈亚,持续了大约6 000万年,以一个巨型时代为特征。从这一时期早期的化石记录丰富了海洋和淡水生物。陆基生物出现在这一时期的中下部分。第一批陆基生物是超大型昆虫和两栖生物。在碳纤维时期的中间,成年两栖动物长达6米,在这一期间结束时形成了蜥蜴的典型毛骨悚然皮肤。Arthropleura,类似于2.6米长的长毫升,在后期碳纤维时期扩散,仍然是有史以来发现的最大的无脊椎动物。

    The Carboniferous period also  gave rise to the largest-known flying insect: the Bolsover dragonfly. The Bolsover dragonfly looks nearly identical to the dragonflies common today, but with a wingspan of 30 cm - six times larger than a modern dragonfly. With a wingspan  this large, the Bolsover dragonfly would not  be able to fly in today's atmosphere,  with 21% oxygen. This has been used to suggest that atmospheric oxygen levels  may have been as high as 30% during the Carboniferous period.  Increased levels of oxygen as well as a generally moister environment  would explain the large size of organisms at the time. Respiration was likely more efficient so that o rganisms could produce more energy and sustain their larger sizes.
    ::碳纤维时代也产生了最著名的飞行昆虫:波尔索弗。波尔索弗看起来与今天常见的几乎相同,但翅膀宽30厘米,比现代的大六倍于30厘米。有了这么大的翅膀,波尔索弗不能在今天的大气中飞行,氧气为21%。这被用来表明在碳纤维时期,大气氧气水平可能高达30%。氧气水平的提高以及一般的麻木环境可以解释当时生物体积的大小。呼吸可能更有效率,这样生物就可以产生更多的能量并保持更大的体积。

     

     

    A fossil of the Bolsover dragonfly, also known as the Meganeura. With a wing span of 30 cm (or nearly a foot), please read the "mega" in meganeura with extra emphasis.
    ::Bolsover 的化石,又称梅根乌拉(Meganeura ) 。 翅膀长30厘米( 或近一英尺), 请阅读特大奈拉的“ mega ” ( mega ) , 特别加强调 。

    As life continued to evolve and diversify, ecosystems began to resemble the types of settings we are familiar with today. This penchant for giantism continued into the   Mesozoic era, which spanned from 252 to 66 Mya and is known as "the Age of the Dinosaurs.'' The   Cenozoic era  that followed saw the  emergence  of mammals . The end of each period during the Phanerozoic Eon was marked by mass extinction events that completely upended the biological landscape of the time.
    ::随着生命的不断演变和多样化,生态系统开始与我们今天熟悉的环境类型相似。这种巨型主义的魔力一直延续到Mesozoic时代,这个时代从252年到66年,被称为“恐龙时代 ” 。 随之而来,出现了哺乳动物。在Phanerozoic Eon的每一个时期的结束,其标志是大规模灭绝事件,完全提升了当时的生物景观。