In a article on Phys, they report scientists have found clues in Alaska that has them rethinking how to continental crust forms based upon research published in Nature Geoscience.
A new study appearing in this week’s Nature Geoscience raises questions about one popular theory and provides new support for another, in which arc lava from the surface and shallow “plutons” – magma that solidified without erupting – are pulled down into the Earth at subduction zones and then rise up to accumulate at the bottom of the arc crust like steam on a kitchen ceiling. Scientists have found compelling evidence to suggest that this could have produced the vast majority of lower continental crust through Earth history.
The process, called relamination, starts at the edge of a continental plate, where an oceanic plate is diving under the continental plate and magma is rising to form a volcanic arc. As the oceanic plate dives, it drags down sediment, lava and plutonic rock from the edge of the arc. As arc material descends, minerals within it become unstable with the rising pressure and heat, and they undergo chemical changes. New minerals form, and chunks of the rock and sediment can break off. When those chunks are denser than the mantle rock around them, they continue to sink. But when they are less dense, such as those that form silica-rich granulites, they become buoyant and float upward until they reach the bottom of the arc crust and accumulate there.
For more information, see:
A new study and timeline has been released showing 190 million years of tetrapod biodiversity, exceptional data for fossils and paleontology.
Recently, we have been able to provide some answers to the questions of how diverse through time has life been, based on the building of large fossil occurrence databases and new methods of analysing them. One such development has been the Paleobiology Database, a professional crowd-sourced archive of fossil history, where the context of fossils is provided in both space and time, and largely based on the published record of fossil discoveries.
…By applying SQS with our development of large fossil occurrence datasets, voila, we are able to gain renewed insight into the diversity of life through history in a way that accounts for the inherent biases of the fossil record!
And that’s just what a new study in PLOS Biology set out to do. Led by Roger Benson of the University of Oxford, an international team of researchers applied SQS to one of the largest tetrapod fossil occurrence databases ever assembled (if not the largest!), comprising more than 27,000 individual fossil occurrences! This represented almost 5000 fossil species, and the data were restricted to just those fossils that dwelled on land – so this excludes groups like ichthyosaurs and plesiosaurs, for example. They also excluded flying tetrapods, so birds, bats and mammals, as these are known to have very different preservational histories in the fossil record. For palaeontology though, this is definitely ‘big data’.
The team restricted their analyses to just the Mesozoic to early Paleogene, a time span of around 190 million years (a fairly long time, even by geological standards!). If you think about it, that’s 5000 species over about 190 million years, which compared to 30,000 around today is pretty weird even in itself.
For more information:
A press release on EurekaAlert, “Deep Carbon: Quest underway to discover its quantity, movements, origins and forms in Earth,” states that the The Deep Carbon Observatory 10-year project to explore the carbon found deep under the earth’s surface.
The program is investigating deep carbon’s movement in the slow convection of the mantle, the percolating fluids of the crust, and the violent emission from volcanoes. It searches for the ancient origin of the deep carbon, and the formation and transformation of its many forms, ranging from gas and oil to diamonds and deep microbes.
Ninety percent or more of Earth’s carbon is thought to be locked away or in motion deep underground–a hidden dimension of the planet as poorly understood as it is profoundly important to life on the surface, according to scientists probing the world’s innermost secrets in the decade-long, $500 million project.
In a landmark volume, DCO scientists say estimates of carbon bound in the metallic core alone range from 0.25 to 1 percent by weight. If 1 percent proves correct, the core by itself sequesters four times more carbon than all known carbon reservoirs in the rest of the planet–and 50,000,000 times as much as that held in the flora and fauna on Earth’s relatively wafer-thin skin far above.
Studies of meteorites suggest that the material that first formed Earth contained about 3% by weight carbon. Confirmed sources of Earth’s carbon, however — life, carbonate rocks like limestone, and carbon dioxide in the oceans and atmosphere — sum to only about 0.1% carbon content.
Carbon is the only element on earth so central to life on the planet, and the research into understanding how carbon influenced life may tell us even more about life evolving on this planet and elsewhere in space.
For more information on the The Deep Carbon Observatory, see:
Updated Jan 2016