Molecular fossils and toxic ancient oceans

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Today, Earth's oceans are teaming with life, and even deep marine trenches contain enough oxygen to support complex organisms. However, oceans in Earth's distant past were fundamentally different. In the first half of Earth history, 4.5 to 1.8 billion years ago, the world's oceans were almost entirely devoid of oxygen.

Astonishingly, for the following one billion years, the state of the oceans remains mysterious. Did the deep oceans become oxygen-rich, in parallel with the Earth's atmosphere, or did they remain anoxic and additionally become sulphidic and toxic? If the world oceans really were anoxic and sulphidic in Earth's middle age, then our understanding of more than 20% of the planet's history would radically change. It would alter our views of global geochemical cycles and may explain why higher forms of life appeared late in Earth history.

In this PhD project, you will elucidate the existence of sulfidic oceans using biomarker molecules extracted from 2.5 to 0.6 billion-years-old sedimentary rocks from Australia, North America and Asia. Biomarkers are the fossil remains of biological molecules. They yield information about the ecology and environment of ancient microbial organisms that lived 1,000 million years before the first animals appeared on Earth.

This will be an exciting multidisciplinary project if you have studied geology, chemistry or biology and are interested in evolution and Earth history. It includes geochemical laboratory work and field studies at locations in the world where the oldest biomarkers may be discovered.

Contact the supervisor directly for more information.

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