Evolution

Rock Soup

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Science  09 May 2014:
Vol. 344, Issue 6184, pp. 558
DOI: 10.1126/science.344.6184.558-b

The fossil record of ancient microorganisms is difficult to disentangle, but the consensus is that complex life on Earth emerged during the Archean Eon, between 2.5 and 4 billion years ago. However, several biochemical processes, including the prebiotic synthesis of proteins and nucleic acids, must already have been established to form the structural and genetic basis of even the simplest life forms. The evolution of metabolic pathways is equally perplexing, yet was essential to allow life to develop autotrophy and adapt to different environments. Keller et al. exposed phosphorylated sugar intermediates—metabolites that form abiotically—to the harsh temperatures and chemical environment that were probably present in Earth's earliest oceans. With metals such as iron acting as catalysts instead of enzymes, they observed 29 interconversion reactions, including the formation of ribose 5-phosphate: the molecule that forms the backbone of RNA. Additionally, the formation of triose-, tetrose-, pentose-, hexose-, and sedoheptulose phosphates, which are components of modern central carbon metabolism, is consistent with the idea that metabolic reaction networks are of primordial origin and developed as a result of the specific geochemical environments present on early Earth.

Mol. Syst. Biol. 10, 725 (2014).

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