A new study by University of Wisconsin Oshkosh geologist Timothy Paulsen and Michigan Tech geologist Chad Deering advances understanding of the role continents have played in the chemical evolution of Earth’s oceans, with implications for understanding atmospheric oxygenation and global climate oscillations.
The team of researchers analyzed a global database of the chemistry of tiny zircon grains commonly found in records of Earth’s continental rocks. The research team includes other scientists from Michigan Technological University and ETH Zurich in Switzerland.
The study made the cover of the February issue of The AGK today by the Geological Society of America.
“Oceans cover 70% of Earth’s surface, which sets it apart from other terrestrial planets in the solar system,” said Paulsen, the paper’s lead author. “Geologists have long recognized that there have been profound changes in ocean chemistry over time.”
Yet there are important questions about the drivers of changes in ocean chemistry in Earth’s past, particularly associated with ancient rock records leading up to the Cambrian explosion of life around 540 million years ago. .
“Continents tend to be weathered and rivers tend to transport these sediments to the oceans, leaving scattered puzzle pieces for geologists to put together,” said Deering, co-author of the paper. “There is growing evidence that important pieces of the puzzle lie in ancient beach and river sediments produced by continental weathering and erosion.”
Researchers’ findings, based on analysis of an exceptionally large dataset of zircons from sandstones recovered from Earth’s major landmasses, could point to key links in the evolution of Earth’s rock cycle and its oceans.
“Our results suggest that two major increases in continental inflow from rivers draining continents were related to continental break-up and dispersal, which caused increased weathering and erosion of a higher proportion of radiogenic rocks and of high altitude continental crust,” Paulsen mentioned.
“Both episodes are curiously associated with terrestrial snowball glaciations and associated stages of oxygenation of the atmosphere-ocean system. Geologists have long recognized that oceans are necessary to make continents. It would seem, according to our analyses, that the continents, in turn, shape the Earth’s oceans, atmosphere and climate.”
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Timothy Paulsen et al, Continental magmatism and uplift as a primary driver of first-order 87Sr/86Sr ocean variability with implications for global climate and atmospheric oxygenation, The AGK today (2021). DOI: 10.1130/GSATG526A.1
Provided by University of Wisconsin Oshkosh
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