October Meeting: Origins of Life and Possibility of Life Elsewhere
The main presentation of our October monthly meeting will be How and when did life start on Earth and what does that indicate for the possibility of life elsewhere? by Professor David Moriarty
A summary of the talk is below.
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From research in the fields of geology, geochemistry, biochemistry and molecular biology, we know that life started very early in Earth’s history. The Earth would have been habitable by about 4.3 billion years ago, i.e. about 300 million years after it formed. Life is based on networks of chemical reactions in cells of all organisms, using energy generated from electrochemical gradients of protons across membranes. The development of biochemistry from geochemistry is evidenced by the role of metal catalysts, in particular iron, nickel and copper, in electron transfer and synthesis of complex organic molecules. The rock record does not extend into the Hadean aeon 4 billion years ago and is fragmented in the Archaean aeon (3 to 4 billion years ago); rocks are transformed, compressed, heated, eroded and recycled. The earliest stromatolites date from 3.7 billion years ago and the oldest microbial fossils from 3.43 billion years ago. Stable carbon isotope ratios of 13C/12C in graphite and carbonates indicate life had started by 4.1 billion years ago.
The first microbes were anaerobic: there was no free oxygen in the water or atmosphere. They obtained their energy by using hydrogen to reduce carbon dioxide and produce organic molecules. For the evolution of complex higher organisms the transfer of electrons to oxygen is essential for the generation of the large amounts of energy needed. Oxygen was not present in sufficient concentration until about 2.4 billion years ago for the first protozoans to evolve and not at a high enough concentration for multicellular organisms to evolve until about 700 million years ago. A complex sequence of biological symbiotic events was needed for complex organisms to evolve, which makes it unlikely that intelligent life might be present elsewhere in our Galaxy or beyond.