Chemical evolution of the proterozoic biosphere

元古代生物圈的化学演化

• 批准号: NE/C518465/2
• 负责人: Simon Poulton
• 金额: $ 3.69万
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FC518465%2F2
• 关键词: Chemical; evolution; proterozoic; biosphere

The surface of the present day Earth is characterised by high levels of oxygen. This is vital to sustain many forms of life on Earth. By contrast, when life first evolved the atmosphere and oceans contained essentially no oxygen. Under these conditions, only certain types of bacteria were able to survive. Various lines of evidence suggest that the oxygen content of the atmosphere only began to rise about 2.3 billion years ago, but at this time the atmosphere still contained much lower amounts of oxygen than at present. Until recently it was thought that this also led to oxygenation of the ocean (as in the present day), which is the environment where early life formed. However, higher life forms such as algae (and ultimately humans), only began to evolve much later. Recently it has been proposed that the oceans did not become oxygenated after the initial rise in atmospheric oxygen. Instead, the increase in oxygen led to the weathering of sulfide minerals on the land, which resulted in increased riverine delivery of sulfur to the oceans. The oceans then became rich in hydrogen sulfide rather than oxygen (similar conditions are found in the modem day Black Sea). Hydrogen sulfide is highly toxic to many life forms, and thus the development of an ocean rich in hydrogen sulfide helps to explain the much later evolution of higher life forms. In fact, the ocean may only have became oxygenated following a second, much later rise in oxygen. This second rise in oxygen broadly coincides with an 'explosion' of life on Earth, and thus indicates a dose link between oxygenation and biological evolution. However, the idea that the oceans contained hydrogen sulfide for a long period of Earth's early history is highly controversial, and further studies are required to test whether such conditions did in fact exist. It is also important to determine how widespread these conditions were (i.e. was the entire ocean rich in hydrogen sulfide), and to determine the precise time when the ocean eventually became oxygenated. Fortunately, it is possible to answer these questions by a detailed chemical examination of rocks which were deposited in the oceans at this time. For a large period of Earth's early history, a type of rock called a 'banded iron formation' was deposited in the oceans. These are rocks which contain a large proportion of iron-rich minerals, and such rocks do not form in the modem environment. It is believed that these rocks could only form in an ocean containing very low amounts of oxygen. Some time after the rise in atmospheric oxygen around 2.3 billion years ago the deposition of banded iron formations abruptly stopped. This project will examine rocks formed during the final stages of the deposition of banded iron formations on Earth. Such rocks are available for scientific research largely because of the previous drilling of rock cores from significant depths below the Earth's surface, in order to find suitable sites for the economic exploitation of minerals. By examining the type of iron-and sulfur-containing minerals in banded iron formations and in overlying oceanic sediments, the nature of the change in ocean chemistry at this time will be evaluated. In addition, the length of time that such conditions lasted will be explored by examining rocks deposited between the two periods of rising atmospheric oxygen. New techniques will be developed and applied to all of the rocks studied, with a particular aim to identify the changing nature of ocean chemistry on a global scale. This research should ultimately provide a better understanding of the links between atmospheric oxygen, ocean chemistry, and the evolution of life on Earth. In doing so, a better understanding of the conditions necessary for life to exist elsewhere in the universe will be achieved.

当今地球表面的特点是含氧量高。这对维持地球上许多生命形式至关重要。相比之下，当生命最初进化时，大气和海洋基本上不含氧气。在这种条件下，只有某些类型的细菌能够存活。各种各样的证据表明，大气中的氧含量在大约23亿年前才开始上升，但此时大气中的氧含量仍然比现在低得多。直到最近，人们还认为这也导致了海洋的氧化作用（就像现在一样），这是早期生命形成的环境。然而，更高的生命形式，如藻类（最终是人类），只是在更晚的时候才开始进化。最近有人提出，在大气中氧气最初增加之后，海洋并没有变成含氧的。相反，氧气的增加导致了陆地上硫化物矿物的风化，这导致了河流向海洋输送硫的增加。随后，海洋中硫化氢的含量比氧气的含量高（在今天的黑海中也发现了类似的情况）。硫化氢对许多生命形式都是剧毒的，因此富含硫化氢的海洋的发展有助于解释高级生命形式后来的进化。事实上，海洋可能只是在一秒钟之后才变成含氧的，而且是在更晚的时候。氧气含量的第二次上升与地球上生命的“大爆发”大致一致，因此表明了氧合作用与生物进化之间的剂量联系。然而，在地球早期历史的很长一段时间里，海洋中含有硫化氢的观点是极具争议的，需要进一步的研究来检验这样的条件是否确实存在。同样重要的是要确定这些条件有多普遍（即整个海洋是否富含硫化氢），并确定海洋最终成为含氧的精确时间。幸运的是，通过对当时沉积在海洋中的岩石进行详细的化学检查，有可能回答这些问题。在地球早期历史的很长一段时间里，一种被称为“带状铁地层”的岩石沉积在海洋中。这些岩石含有大量富含铁的矿物，而这种岩石不是在现代环境中形成的。据信，这些岩石只能在含氧量极低的海洋中形成。大约23亿年前，在大气中氧气含量上升后的一段时间里，带状铁的沉积突然停止了。这个项目将检查在地球上带状铁地层沉积的最后阶段形成的岩石。这些岩石可以用于科学研究，很大程度上是因为以前为了寻找适合矿物经济开采的地点，从地球表面下很深的地方钻取岩心。通过检查带状铁地层和上覆海洋沉积物中含铁和含硫矿物的类型，可以评估此时海洋化学变化的性质。此外，这种条件持续的时间长度将通过检查在两个大气氧气上升时期之间沉积的岩石来探索。将开发新技术，并将其应用于所研究的所有岩石，其特别目的是确定全球范围内海洋化学性质的变化。这项研究最终将使我们更好地了解大气氧气、海洋化学和地球生命进化之间的联系。这样一来，我们就能更好地了解宇宙中其他地方生命存在的必要条件。

项目成果

A continental-weathering control on orbitally driven redox-nutrient cycling during Cretaceous Oceanic Anoxic Event 2

• DOI: 10.1130/g36837.1
• 发表时间: 2015-11
• 期刊: Geology
• 影响因子: 5.8
• 作者: S. Poulton;S. Henkel;C. März;H. Urquhart;S. Flögel;S. Kasten;J. Damsté;T. Wagner

Cretaceous Ocean Redbeds - Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance

白垩纪海洋红层 - 地层学、成分、起源以及古海洋学和古气候意义

• DOI: 10.2110/sepmsp.091.223
• 发表时间: 2009
• 作者: HUANG Y