Earth Science Research Seminar: Dr Alex Brasier

Earth Science Research Seminar: Dr Alex Brasier
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This is a past event

The evolving impacts of the biosphere on the geosphere and hydrosphere, from Earth's oldest fossils to last October

Please join us for a seminar given by Dr. Alex Brasier (UoA) on 'The evolving impacts of the biosphere on the geosphere and hydrosphere, from Earth’s oldest fossils to last October'.

Abstract:

Earth is 4600 000 000 years old. I am thirty three. The only way to really understand where we (organisms) came from, and where we are going, is to look at the evidence preserved in rocks. This story begins with a critical re-examination of what were long called Earth’s oldest fossil organisms (M.D.Brasier et al., 2002; 2015; Wacey et al., 2015), and chemical evidence for early life >3.5 billion years ago. I will then leap forwards one billion years to ‘Planet Earth’s mid-life crisis’. Here, 2.4 to 1.9 billion years ago, rising atmospheric oxygen levels from oxygenic photosynthesis possibly caused a global ‘snowball Earth’ glaciation (Brasier et al., 2013) and then turned the planet toxic for most of their anaerobic microbe friends. In the rocks we see the results of this chemical warfare: sulphate and iron oxide minerals, formed in an atmosphere with free oxygen; carbon isotopes of carbonate rocks compatible with vast volumes of photosynthesising microbes in the oceans (Brasier et al., 2011; in review; and several others) and anaerobic microbes retreating into the ocean sediment, forming new rock types. Another billion years later, we find the first evidence for a terrestrial subterranean biosphere. Forward again, to ~420 million years ago, where we find bigger organisms have evolved, and colonisation of the continents as the undergraduate text-books have it. Decomposition of this plant matter produces limestones in soils, known as calcretes, formed on floodplains of Earth’s first meandering rivers (Brasier et al., 2014). And finally to last October, when I visited Mono Lake, California, searching for the hydrological, biological and geological processes that preserved our ancient ancestors (and their more recent cousins).

Speaker
Dr Alex Brasier
Venue
St Mary's building, Room 105