1.2 The Origin of Life

The origin of life are thought to have occurred sometimebetween 4.4 billion years ago, when the oceans and continents were juststarting to form, and 2.7 billion years ago, when it is widely accepted thatmicroorganisms existed in vast numbers due to their influence over isotope ratios in the relevant strata. Where exactly in this 1.7 billion yearrange the true origin of life can be found is less certain. A controversialpaper published in 2002 by the UCLA paleontologist William Schopfargued that wavy geological formations called stromalites in fact contain 3.5 billion year-old fossilized algae microbes. Some paleontologists disagree with Schopf’sconclusions and estimate the first life at around 3.0 billion years of ageinstead of 3.5 billion.

    Evidence from the Isua supracrustal belt in Western Greenland suggests aneven earlier date for the origin of life - 3.85 billion years ago. S. Mojzismakes this estimate based on isotope concentrations. Because lifepreferentially uptakes the isotope Carbon-12, areas where life has existed containa higher-than-normal ratio of Carbon-12 to its heavier isotope, Carbon-13. Thisis widely known, but the interpretation of sediments is less straightforward, andpaleontologists do not always agree on their colleague’s conclusions.

In the large warm oceans of early Earth, quintillions of these molecules would randomly collide and combine,eventually making a rudimentary proto-genome of some sort. However, this hypothesis is confused by the fact that theenvironment created in the Miller-Urey experiment had high concentrations ofchemicals that would have prevented the formation of complex polymers from the monomer building blocks.

origin of life 生命的起源

isotope ['aisətəup] n. 同位素

strata ['streitə] n. 地层

geological [dʒiə'lɔdʒikəl] adj. 地质学的

stromalite[strəumætlait] n. 叠层石

fossilize ['fɔsilaiz]vt.& vi. 使成化石,使陈腐

algae ['ældʒi:] n. 水藻，海藻 alga的复数形式

microbe ['maikrəub] n. 微生物

paleontologist [pæliɔn'tɔlədʒist] n. 古生物学家

supracrustal [sju:prə'krʌstəl]adj. (地层、岩组等)覆盖基底岩石的, 上地壳的

carbon ['kɑ:bən] n. 碳

sediment ['sedimənt] n. 沉淀

geological condition  地质条件

laboratory ['læbrətɔ:ri]n. 实验室

oxygenate ['ɔksidʒineit]v. 以氧处理,氧化n. 氧化剂

methane ['meθein] n. 甲烷，沼气

ammonia [ə'məunjə] n. 氨

hydrogen ['haidrədʒən] n. 氢

organic [ɔ:'gænik]adj. 器官的,有机的

monomer ['mɔnəmə] n. 单体

amino acid 氨基酸

inorganic ['inɔ:'gænik] adj. 无机的,无生物的

self-replicate ['self'replikeit] v. 自我复制

metabolism [me'tæbəlizəm] n. 新陈代谢

dynamics [dai'næmiks] n. 力学,动力学, 动态

peptide ['peptaid] n. 肽

membrane ['membrein] n. 薄膜，膜状物

proto-cell n. 细胞的原始状态

microsphere ['maikrəsfiə]n. 微球体,微滴

primitive ['primitiv]adj. 原始的,简陋的

self-replication n. 自我复制

Darwinian evolution 达尔文进化

cyanobacteria ['saiænəu'bæktiə] n. 蓝细菌cyanobacterium的复数形式