Chapter 5

Origins of Life and Earth Prehistory

According to current theories, our present universe originated in a big bang that

happened about 14 × 10⁹ years ago. It is believed that this universe started with low

entropy, due to the dominance of the entropy associated with gravity (Lineweaver and

Egan 2012). Low entropy is a prerequisite for allowing life to develop (see Chap. 1).

Earth is believed to have been formed about 4500 million years ago. For the first

500 million years of its existence it was probably rather inhospitable to life, not

least because of the high frequency of asteroid impacts. The early atmosphere was

probably rich in nitrogen, carbon dioxide, sulphur dioxide, and water. Since the sun

was significantly cooler than today, high carbon dioxide content would have been

important for ensuring an abundance of liquid water (which would otherwise have

been frozen). These conditions were probably favourable for the development of

precursors to life. ¹ Following the discovery of exoplanets (Mayor and Queloz 1995)

there has been much interest in identifying those likely to favour the initiation of life

(Meadows et al. 2017, 2018). A key criterion is the inferred presence of liquid water.

An adequate flux of ultraviolet right is needed for the photochemical production of

RNA precursors (Patel et al. 2015; Rimmer et al. 2018).

The first traces of life on Earth—in the sense of an entity resembling a prokary-

otic cell—may date back to as long ago as 4000 million years. Stromatolites—vast

structures of mineralized bacteria—may date back to about 3500 million years ago.

Methanogenic archaea seem to have been active by 3400 million years ago, exac-

erbating the “greenhouse” effect. But primordial photosynthesis, developed in the

course of the succeeding few hundred million years, finally became sophisticated

enough to oxidize water, releasing oxygen into the atmosphere, and culminating in

the “great oxygenation event” now believed to have occurred 2330 million years ago

(Luo et al. 2016).

1 See, e.g., Patel et al. (2015).

© Springer Nature Switzerland AG 2023

J. Ramsden, Bioinformatics, Computational Biology,

https://doi.org/10.1007/978-3-030-45607-8_5

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