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Large landmasses existed 2.7 billion years ago

Date:
January 15, 2014
Source:
University of Cologne - Universität zu Köln
Summary:
Some 71 percent of Earth's surface is covered by oceans and 29 percent by land. The question of when large landmasses emerged from the oceans has always been hotly debated. New investigations by geoscientists have shown that large land masses did indeed exist on Earth 2.7 billion years ago.
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Some 71% of Earth's surface is covered by oceans and 29% by land. The question of when large landmasses emerged from the oceans has always been hotly debated by scientists. New investigations by geoscientists of the University of Cologne in cooperation with the University of Bonn and the Jacobs University Bremen have shown that large land masses did indeed exist on Earth 2.7 billion years ago

A Cologne working group involving Prof. Carsten Münker and Dr. Elis Hoffmann and their student Sebastian Viehmann (working with Prof. Michael Bau from the Jacobs University Bremen) have managed for the first time to determine the isotope composition of the rare trace elements Hafnium and Neodymium in 2.7-billion-year-old seawater by using high purity chemical sediments from Temagami Banded Iron Formation (Canada) as an archive.

Earlier work has shown that these rocks from Canada only contain chemical elements that directly precipitated from ocean water. The Temagami Banded Iron Formation, which was formed 2.7 billion years ago during the Neoarchean period, can be used as an archive because the isotopic composition of many chemical elements such as Hafnium and Neodymium directly mirrors the composition of Neoarchean seawater. These two very rare elements allow many valuable conclusions about weathering processes to be drawn.

During their investigations, the research team came to the surprising result that has been published in the journal Geology: 2.7 billion years ago, seawater contained an unusually high abundance of the radioactive isotope Hafnium 176 but a comparably low abundance of the radioactive isotope Neodymium 143, similar to what can be observed in present day seawater.

"In present day seawater, this can be explained by weathering and the erosion of the Earth's exposed surface," explains Prof. Münker. "If in the Neoarchean period 97% of the Earth's surface had been, as estimated from computer models, covered by water, these geochemical signals would not have been found for Neoarchean seawater," adds Dr. Hoffmann.

According to the scientific team, the new findings show that 2.7 billion years ago relatively large landmasses emerged from the oceans that were exposed to weathering and erosion by the sun, wind and rain. Dr. Hoffmann: "The isotope Hafnium 176 in contrast to its counterpart Neodymium 143 was transported by means of weathering into the oceans and became part of iron-rich sediments on the sea floor 2,700 million years ago."

The examinations were carried out in the joint clean laboratory of the Universities of Cologne and Bonn. Prof. Münker: "We are able to carry out these isotope measurements for very rare elements, the concentrations of which are in the ppb range, i.e. only a few parts per billion."


Story Source:

The above post is reprinted from materials provided by University of Cologne - Universität zu Köln. Note: Materials may be edited for content and length.


Journal Reference:

  1. S. Viehmann, J. E. Hoffmann, C. Munker, M. Bau. Decoupled Hf-Nd isotopes in Neoarchean seawater reveal weathering of emerged continents. Geology, 2013; DOI: 10.1130/G35014.1

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University of Cologne - Universität zu Köln. "Large landmasses existed 2.7 billion years ago." ScienceDaily. ScienceDaily, 15 January 2014. <www.sciencedaily.com/releases/2014/01/140115075414.htm>.
University of Cologne - Universität zu Köln. (2014, January 15). Large landmasses existed 2.7 billion years ago. ScienceDaily. Retrieved July 4, 2015 from www.sciencedaily.com/releases/2014/01/140115075414.htm
University of Cologne - Universität zu Köln. "Large landmasses existed 2.7 billion years ago." ScienceDaily. www.sciencedaily.com/releases/2014/01/140115075414.htm (accessed July 4, 2015).

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