New research suggests that the geological staying power of continents comes partly from their losing battle with the Earth's oceans over magnesium. The research finds continents lose more than 20 percent of their initial mass via chemical reactions involving the Earth's crust, water and atmosphere. Because much of the lost mass is dominated by magnesium and calcium, continents ultimately gain because the lighter, silicon-rich rock that's left behind is buoyed up by denser rock beneath the Earth's crust.
The Earth's continents seem like fixtures, having changed little throughout recorded human history. But geologists know that continents have come and gone during the Earth's 4.5 billion years. However, there are more theories than hard data about some of the key processes that govern continents' lives.
"Continents are built by new rock that wells up from volcanoes in island arcs like Japan," said lead author Cin-Ty Lee, assistant professor of Earth science at Rice University. "In addition to chemical weathering at the Earth’s surface, we know that some magnesium is also lost due to destabilizing convective forces beneath these arcs."
Lee's research, which appeared in the March 24 issue of the Proceedings of the National Academy of Science, marks the first attempt to precisely nail down how much magnesium is lost through two markedly different routes -- destabilizing convective forces deep inside the Earth and chemical weathering reactions on its surface. Lee said the project might not have happened at all if it weren't for some laboratory serendipity.
"I'd acquired some tourmaline samples in San Diego with my childhood mentor, Doug Morton," Lee said. "We were adding to our rock collections, like kids, but when I got back to the lab, I was curious where the lithium, a major element in tourmaline, needed to make the tourmalines came from. I decided to measure the lithium content in the granitic rocks from the same area, and that's where this started."
In examining the lithium content in a variety of rocks, Lee realized that lithium tended to behave like the magnesium that was missing from continents. In fact, the correlation was so close, he realized that lithium could be used as a proxy to find out how much magnesium continents had lost due to chemical weathering.
Continents ride higher than oceans, partly because the Earth's crust is thicker beneath continents than it is beneath the oceans. In addition, the rock beneath continents is made primarily of silicon-rich minerals like granite and quartz, which are less dense than the magnesium-rich basalt beneath the oceans.
Lee said he always assumed that processes deep in the Earth, beneath the volcanoes that feed continents, accounted for far more magnesium loss than weathering. In particular, a process called "delamination" occurs in subduction zones, places where one piece of the Earth's crust slides beneath another and gets recycled into the Earth's magma. As magma wells up beneath continent-feeding volcanoes, it often leaves behind a dense, magnesium-rich layer that ultimately founders back into the Earth's interior.
In previous research, Lee found that about 40 percent of the magnesium in basaltic magma was lost to delamination. He said he was thus surprised to find that chemical weathering alone accounted for another 20 percent.
"Weathering occurs in just the top few meters or so of the Earth's crust, and it's driven by the hydrosphere, the water that moves between the air, land and oceans," Lee said. "It appears that our planet has continents because we have an active hydrosphere, so if we want to find a hydrosphere on distant planets, perhaps we should look for continents."
Jade Boyd | EurekAlert!
More than 100 years of flooding and erosion in 1 event
28.03.2017 | Geological Society of America
Satellites reveal bird habitat loss in California
28.03.2017 | Duke University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy