Archives de catégorie : only geology

Volcanoes fed by ‘mush’ reservoirs rather than molten magma chambers

by Imperial College London, December 4, 2018 in ScienceDaily

Volcanoes are not fed by molten magma formed in large chambers finds a new study, overturning classic ideas about volcanic eruptions.

Instead, the study suggests that volcanoes are fed by so-called ‘mush reservoirs’ — areas of mostly solid crystals with magma in the small spaces between the crystals.

Our understanding of volcanic processes, including those leading to the largest eruptions, has been based on magma being stored in liquid-filled ‘magma’ chambers — large, underground caves full of liquid magma. However, these have never been observed.

The new study, by researchers at Imperial College London and the University of Bristol and published today in Nature, suggests the fundamental assumption of a magma chamber needs a re-think.

Oxygen could have been available to life as early as 3.5 billion years ago

by Imperial College, November 27, 2018 in ScienceDaily

The levels of oxygen dramatically rose in the atmosphere around 2.4 billion years ago, but why it happened then has been debated. Some scientists think that 2.4 billion years ago is when organisms called cyanobacteria first evolved, which could perform oxygen-producing (oxygenic) photosynthesis.

Other scientist think that cyanobacteria evolved long before 2.4 billion years ago but something prevented oxygen from accumulating in the air.

Cyanobacteria perform a relatively sophisticated form of oxygenic photosynthesis — the same type of photosynthesis that all plants do today. It has therefore been suggested that simpler forms of oxygenic photosynthesis could have existed earlier, before cyanobacteria, leading to low levels of oxygen being available to life.

Now, a research team led by Imperial College London have found that oxygenic photosynthesis arose at least one billion years before cyanobacteria evolved. Their results, published in the journal Geobiology, show that oxygenic photosynthesis could have evolved very early in Earth’s 4.5-billion-year history.

See also here

Meeting Plate Tectonics – Peter Molnar

by D. Fernandez-Blanco, November 20, 2018 in EGU

What do you think are the biggest challenges right now in your field?

Some of the challenges are too hard for me even to pursue them. In the climate world, we don’t know about the role of clouds. And I don’t know how to pursue this, so I don’t pursue it. Do clouds have a cooling effect, and what is the response from clouds to warming? Will they slow or accelerate the warming? We don’t know. The role of clouds is certainly a big, big question. Although I do not work on this, I think about it, but I don’t see what to do.

One of the problems I do work on is what brought us Ice Ages. How did we go through 300 My years without much ice in the northern hemisphere and then suddenly, beginning 3My years ago or so, we had 5 big Ice Ages? Why? An easy answer is that now CO2 is higher. But it’s really hard to measure, determining CO2 in the past is a big question.

Another big question for me is how does the convection in the mantle connect with deformation in the lithosphere? How do these connect to one another?

Relics of ‘lost continents’ hidden under Antarctica are revealed by satellite images after scientists track 200 million years of tectonic plate shifts

by H. Pettit, November 9, 2018 in MailOnline

  • Images reveal a timeline of the ancient landmasses buried beneath Antarctica
  • They were taken by the long-dead Gravity field and Ocean Circulation Explorer 
  • The ESA satellite collected data on Earth’s gravitational pull

  • The study revealed that West Antarctica (green) has a thinner crust than East Antarctica (blue), which has a ‘family likeness to Australia and India’

USGS issues first USA Volcano Threat Assessment in over a decade

by Anthony Watts, October 24, 2018 in WUWT

18 volcanoes in the USA are classified as “very high threat”, many are in the Pacific Northwest.

Here the .pdf (USGS, 2018)

The United States has 161 young, active volcanoes within its borders. Since 1980, there have been 120 eruptions and 52 episodes of notable volcanic unrest at 44 U.S. volcanoes.

The U.S. Geological Survey systematically assesses U.S. volcanoes considered to be active or potentially active, and publishes a volcanic threat assessment that ranks the volcanoes based on 24 hazard and exposure factors. Last published in 2005, this 2018 update considers (1) field and laboratory research that adds or removes volcanoes from the list of potentially active volcanoes, and (2) updates the hazard and exposure factors used to produce a relative threat ranking of volcanoes.

Lessons from Dutch geological history might be useful for other present-day deltas

by Geological Society of America, October 9, 2018 in ScienceDaily 

Even long before medieval inhabitants reclaimed land and raised dykes at a large scale, humans have had a strong impact on river behavior in the Dutch delta plain. Physical geographers have demonstrated that two present Rhine branches developed stepwise in the first centuries CE, because of two combined man-induced effects.

Plate tectonics may have been active on Earth since the very beginning

by University of Tennessee at Knoxville, September 26, 2018 in ScienceDaily

A new study suggests that plate tectonics — a scientific theory that divides the earth into large chunks of crust that move slowly over hot viscous mantle rock — could have been active from the planet’s very beginning. The new findings defy previous beliefs that tectonic plates were developed over the course of billions of years.

The paper, published in Earth and Planetary Science Letters, has important implications in the fields of geochemistry and geophysics. For example, a better understanding of plate tectonics could help predict whether planets beyond our solar system could be hospitable to life.

“Plate tectonics set up the conditions for life,” said Nick Dygert, assistant professor of petrology and geochemistry in UT’s Department of Earth and Planetary Sciences and coauthor of the study. “The more we know about ancient plate tectonics, the better we can understand how Earth got to be the way it is now.”

Geologists reveal ancient connection between England and France

by University of Plymouth, September 14, 2018 in ScienceDaily

The British mainland was formed from the collision of not two, but three ancient continental land masses, according to new research.

Scientists have for centuries believed that England, Wales and Scotland were created by the merger of Avalonia and Laurentia more than 400 million years ago.

However, geologists based at the University of Plymouth now believe that a third land mass — Armorica — was also involved in the process.

The findings are published in Nature Communications and follow an extensive study of mineral properties at exposed rock features across Devon and Cornwall …

Credit: University of Plymouth

Geologists uncover new clues about largest mass extinction ever

by University of Tennessee at Knoxville, August 27, 2018 in ScienceDaily from Nature.

Through the analysis of samples, Broadley and his team tried to determine the composition of the lithosphere. They found that before the Siberian Flood Basalts took place, the Siberian lithosphere was heavily loaded with chlorine, bromine, and iodine, all chemical elements from the halogen group. However, these elements seem to have disappeared after the volcanic eruption.

“We concluded that the large reservoir of halogens that was stored in the Siberian lithosphere was sent into the earth’s atmosphere during the volcanic explosion, effectively destroying the ozone layer at the time and contributing to the mass extinction,” Broadley said.

Research into deadly 2016 Italian earthquakes could improve future seismic forecasts

by Durham University, Augsut23, 2018 in ScienceDaily

The timing and size of three deadly earthquakes that struck Italy in 2016 may have been pre-determined, according to new research that could improve future earthquake forecasts.

A joint British-Italian team of geologists and seismologists have shown that the clustering of the three quakes might have been caused by the arrangement of a cross-cutting network of underground faults.

The findings show that although all three earthquakes occurred on the same major fault, several smaller faults prevented a single massive earthquake from occurring instead and also acted as pathways for naturally occurring fluids that triggered later earthquakes.

Integrated genomic and fossil evidence illuminates life’s early evolution and eukaryote origin

by Holly C. Betts et al., August 20, 2018 in NatureEcology&Evolution

We derive a timescale of life, combining a reappraisal of the fossil material with new molecular clock analyses. We find the last universal common ancestor of cellular life to have predated the end of late heavy bombardment (>3.9 billion years ago (Ga)). The crown clades of the two primary divisions of life, Eubacteria and Archaebacteria, emerged much later (<3.4 Ga), relegating the oldest fossil evidence for life to their stem lineages. The Great Oxidation Event significantly predates the origin of modern Cyanobacteria, indicating that oxygenic photosynthesis evolved within the cyanobacterial stem lineage. Modern eukaryotes do not constitute a primary lineage of life and emerged late in Earth’s history (<1.84 Ga), falsifying the hypothesis that the Great Oxidation Event facilitated their radiation…

Chemical nature of the 3.4 Ga Strelley Pool microfossils

by J. Allen et al., 2018 in GeochemicalPerspectiveLetters

The biogenicity of putative traces of life found in early-Archean rocks is strongly debated. To date, only equivocal lines of evidence have been reported, which has prevented a full consensus from emerging. Here we report elemental and molecular data from individual organic microfossils preserved within the 3.4 billion-year-old cherts of the Strelley Pool Formation, Western Australia. The present results support the growing body of evidence advocating their biogenicity, promoting them as the oldest known authentic organic microfossils. These microfossils consist of nitrogen- and oxygen- rich organic molecules that have been only slightly degraded despite experiencing temperatures of ~300 °C. Such molecular preservation emphasises the palaeobiological potential of the Earth’s oldest geological record, whilst providing a promising window into the early biosphere.

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Billion-year-old lake deposit yields clues to Earth’s ancient biosphere

by McGill University, July 18, 2018 in ScienceDaily

The findings, published in the journal Nature, represent the oldest measurement of atmospheric oxygen isotopes by nearly a billion years. The results support previous research suggesting that oxygen levels in the air during this time in Earth history were a tiny fraction of what they are today due to a much less productive biosphere.

“It has been suggested for many decades now that the composition of the atmosphere has significantly varied through time,” says Peter Crockford, who led the study as a PhD student at McGill University. “We provide unambiguous evidence that it was indeed much different 1.4 billion years ago.”

The study provides the oldest gauge yet of what earth scientists refer to as “primary production,” in which micro-organisms at the base of the food chain — algae, cyanobacteria, and the like — produce organic matter from carbon dioxide and pour oxygen into the air.

Sound waves reveal diamond cache deep in Earth’s interior

by Jennifer Chu, July 16 in MITNews

There may be more than a quadrillion tons of diamond hidden in the Earth’s interior, according to a new study from MIT and other universities. But the new results are unlikely to set off a diamond rush. The scientists estimate the precious minerals are buried more than 100 miles below the surface, far deeper than any drilling expedition has ever reached.

The ultradeep cache may be scattered within cratonic roots — the oldest and most immovable sections of rock that lie beneath the center of most continental tectonic plates. Shaped like inverted mountains, cratons can stretch as deep as 200 miles through the Earth’s crust and into its mantle; geologists refer to their deepest sections as “roots.”

In the new study, scientists estimate that cratonic roots may contain 1 to 2 percent diamond. Considering the total volume of cratonic roots in the Earth, the team figures that about a quadrillion (1016) tons of diamond are scattered within these ancient rocks, 90 to 150 miles below the surface.