Archives de catégorie : only geology

Meteorite study suggests Earth may have been wet since it formed

by Washington University in St. Louis, Aug 27, 2020 in ScienceDaily


Enstatite chondrite meteorites, once considered ‘dry,’ contain enough water to fill the oceans — and then some

A new study finds that Earth’s water may have come from materials that were present in the inner solar system at the time the planet formed — instead of far-reaching comets or asteroids delivering such water. The findings published Aug. 28 in Science suggest that Earth may have always been wet.

Researchers from the Centre de Recherches Petrographiques et Geochimiques (CRPG, CNRS/Universite de Lorraine) in Nancy, France, including one who is now a postdoctoral fellow at Washington University in St. Louis, determined that a type of meteorite called an enstatite chondrite contains sufficient hydrogen to deliver at least three times the amount of water contained in the Earth’s oceans, and probably much more.

Enstatite chondrites are entirely composed of material from the inner solar system — essentially the same stuff that made up the Earth originally.

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water,” said lead author Laurette Piani, a researcher at CPRG. “Hydrogen-bearing material was present in the inner solar system at the time of the rocky planet formation, even though the temperatures were too high for water to condense.”

Le Précambrien : les bactéries, la tectonique des plaques et l’oxygène

by A. Préat (.pdf), 21 août 2020 in Bull.Séanc.Acad.R.Sci.OutreMer


 Mots-clés. — Écosystèmes microbiens; Isotopes du carbone et du soufre; Oxydoréduction; Oxygène; Océans et atmosphère. 

Résumé. — L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète. Malgré un apport en oxygène lié aux cyanobactéries dès l’archéen, ce ne sont pas ces microorganismes qui sont à la base de la première grande «révolution» de l’oxygène qui a eu lieu à la limite archéen/paléoprotérozoïque (il y a deux milliards et demi d’années) dans l’atmosphère, lors du Grand Événement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique voici deux milliards et demi d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite. L’altération des séries riches de ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’archéen sera remplacée par une atmosphère oxydante à la fin du précambrien. 

Keywords. — Microbial Ecosystems; Carbon and Sulfur Isotopes; Oxidation Reduction; Oxygen; Oceans and Atmosphere. 

Summary. — The Precambrian: Bacteria, Plate Tectonics and Oxygen. — Oxygen did not appear as abruptly as we thought on our planet. Despite an oxygen supply related to cyanobacteria since the Archean, these microorganisms are not at the origin of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (two and a half billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the atmospheric oxygen concentration two and a half billion years ago. These two main processes are related to the burial of organic matter and pyrite. The alteration of series with high contents of these two elements will then condition for nearly one billion years the oxygen, sulfur and iron chemical composition of the oceans. Oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian. 

Fig. 3. — Évolution des compositions chimiques et des organismes des océans en trois phases majeures. À l’archéen, les océans contiennent peu d’oxygène et sont relativement riches en fer (colonne de gauche), alors que dans les océans modernes (colonne de droite) l’oxygène est abondant et le fer en quantité limitée. Entre ces deux phases, un long intervalle d’un peu plus d’un milliard d’années est caractérisé par des océans avec des concentrations modérées d’oxygène en surface et des eaux plus profondes riches en H2S en présence de quantités limitées de fer, de molybdène et d’autres éléments en traces importants dans les cycles biologiques. La colonne centrale représente l’«Océan de Canfield» et caractérise le Boring Billion. L’H2S produit (suite à la présence des sulfates, cf. texte) réagit avec le fer ferreux pour former la pyrite. Le fer ferreux n’est donc pas consommé par l’oxygène durant cet intervalle de temps, mais par l’H2S. L’Événement Lomagundi-Jatuli a lieu à environ 2,1 Ga dans le GOE (Great Oxidation Event), marqué par une très forte production d’oxygène. Le début du GOE est marqué par l’oxydation de la pyrite sur les cratons et la disparition des minéraux détritiques sensibles aux conditions d’oxydoréduction des éléments chalcophiles ou sidérophiles (uraninite, sidérite, pyrite, molybdénite, etc.). Les deux grands épisodes «Terre Boule de Neige» à 2,3 Ga («Glaciation Makganyena») et 0,635 («Glaciation Marinoenne»), et d’autres événements glaciaires moins importants ne sont pas reportés ni discutés dans le texte (modifié d’après Knoll 2003). 

 

World’s Largest Meteorite

by Geology Page, January 8, 2017


Name: Hoba “This is an OFFICIAL meteorite name”
Abbreviation: There is no official abbreviation for this meteorite.
Observed fall: No
Year found: 1920
Country: Namibia
Mass: 60 tons

The Hoba or Hoba West meteorite lies on the farm “Hoba West”, not far from Grootfontein, in the Otjozondjupa Region of Namibia. It has been uncovered but, because of its large mass, has never been moved from where it fell. The main mass is estimated at more than 60 tons, making it the largest known meteorite (as a single piece) and the most massive naturally occurring piece of iron known on Earth’s surface.

Impact

The Hoba meteorite impact is thought to have occurred more recently than 80,000 years ago. It is inferred that the Earth’s atmosphere slowed the object to the point that it impacted the surface at terminal velocity, thereby remaining intact and causing little excavation.

Assuming a drag coefficient of about 1.3, the meteor would have been slowed to about 720 miles per hour (0.32 km/s) from its speed on entering the Earth’s atmosphere, typically in excess of 10 km/s for similar objects. The meteorite is unusual in that it is flat on both major surfaces, possibly causing it to have skipped across the top of the atmosphere like a flat stone skipping on water.

Read more : http://www.geologypage.com/2017/01/worlds-largest-meteorite.html#ixzz6U2Q7UUR8
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Evolution after Chicxulub asteroid impact: Rapid response of life to end-cretaceous mass

by Geological Society of America, July 14, 2020 in ScienceDaily


The impact event that formed the Chicxulub crater (Yucatán Peninsula, México) caused the extinction of 75% of species on Earth 66 million years ago, including non-avian dinosaurs. One place that did not experience much extinction was the deep, as organisms living in the abyss made it through the mass extinction event with just some changes to community structure.

New evidence from International Ocean Discovery Program (IODP) Expedition 364 of trace fossils of burrowing organisms that lived in the seafloor of the Chicxulub Crater beginning a few years after the impact shows just how quick the recovery of the seafloor ecosystem was, with the establishment of a well-developed tiered community within  approximately 700,000 years after the event.

Impact-induced amino acid formation on Hadean Earth and Noachian Mars

by Takeuchi et al., June8, 2020 in SciReports Open Access


Abstract

Abiotic synthesis of biomolecules is an essential step for the chemical origin of life. Many attempts have succeeded in synthesizing biomolecules, including amino acids and nucleobases (e.g., via spark discharge, impact shock, and hydrothermal heating), from reduced compounds that may have been limited in their availabilities on Hadean Earth and Noachian Mars. On the other hand, formation of amino-acids and nucleobases from CO2 and N2 (i.e., the most abundant C and N sources on Earth during the Hadean) has been limited via spark discharge. Here, we demonstrate the synthesis of amino acids by laboratory impact-induced reactions among simple inorganic mixtures: Fe, Ni, Mg2SiO4, H2O, CO2, and N2, by coupling the reduction of CO2, N2, and H2O with the oxidation of metallic Fe and Ni. These chemical processes simulated the possible reactions at impacts of Fe-bearing meteorites/asteroids on oceans with a CO2 and N2 atmosphere. The results indicate that hypervelocity impact was a source of amino acids on the Earth during the Hadean and potentially on Mars during the Noachian. Amino acids formed during such events could more readily polymerize in the next step of the chemical evolution, as impact events locally form amino acids at the impact sites.

Asteroid, climate change not responsible for mass extinction 215 million years ago

by Todd McLeish, May 27, 2020 U. of RhodeIsland in PhysOrg


A team of University of Rhode Island scientists and statisticians conducted a sophisticated quantitative analysis of a mass extinction that occurred 215 million years ago and found that the cause of the extinction was not an asteroid or climate change, as had previously been believed. Instead, the scientists concluded that the extinction did not occur suddenly or simultaneously, suggesting that the disappearance of a wide variety of species was not linked to any single catastrophic event.

Their research, based on paleontological field work carried out in sediments 227 to 205 million years old in Petrified Forest National Park, Arizona, was published in April in the journal Geology.

..

Giant tectonic plate under Indian Ocean is breaking in two

by Geggel L., May 21, 2020 in LiveScience


The giant tectonic plate under the Indian Ocean is going through a rocky breakup … with itself.

In a short time (geologically speaking) this plate will split in two, a new study finds.

To humans, however, this breakup will take an eternity. The plate, known as the India-Australia-Capricorn tectonic plate, is splitting at a snail’s pace — about 0.06 inches (1.7 millimeters) a year. Put another way, in 1 million years, the plate’s two pieces will be about 1 mile (1.7 kilometers) farther apart than they are now.

“It’s not a structure that is moving fast, but it’s still significant compared to other planet boundaries,” said study co-researcher Aurélie Coudurier-Curveur, a senior research fellow of marine geosciences at the Institute of Earth Physics of Paris.

Related: In photos: Ocean hidden beneath Earth’s surface

For instance, the Dead Sea Fault in the Middle East is moving at about double that rate, or 0.2 inches (0.4 centimeters) a year, while the San Andreas Fault in California is moving about 10 times faster, at about 0.7 inches (1.8 cm) a year.

The plate is splitting so slowly and it’s so far underwater, researchers almost missed what they’re calling the “nascent plate boundary.” But two enormous clues — that is, two strong earthquakes originating in a strange spot in the Indian Ocean — suggested that Earth-changing forces were afoot.

On April 11, 2012, a magnitude-8.6 and magnitude-8.2 earthquake hit beneath the Indian Ocean, near Indonesia. The earthquakes didn’t happen along a subduction zone, where one tectonic plate slides under another. Instead, these quakes originated in a weird place for earthquakes to happen — in the middle of the plate.

Scientists “Discover” Largest Shield Volcano on Earth

by D. Middleton, May 15, 2020 in WUWT


And it’s not Mauna Loa…

UH researchers reveal largest and hottest shield volcano on Earth
Posted on May 13, 2020 by Marcie Grabowski

In a recently published study, researchers from the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology revealed the largest and hottest shield volcano on Earth. A team of volcanologists and ocean explorers used several lines of evidence to determine Pūhāhonu, a volcano within the Papahānaumokuākea Marine National Monument, now holds this distinction.

Geoscientists and the public have long thought Mauna Loa, a culturally-significant and active shield volcano on the Big Island of Hawai‘i, was the largest volcano in the world. However, after surveying the ocean floor along the mostly submarine Hawaiian leeward volcano chain, chemically analyzing rocks in the UH Mānoa rock collection, and modeling the results of these studies, the research team came to a new conclusion. Pūhāhonu, meaning ‘turtle rising for breath’ in Hawaiian, is nearly twice as big as Mauna Loa.

“It has been proposed that hotspots that produce volcano chains like Hawai‘i undergo progressive cooling over 1-2 million years and then die,” said Michael Garcia, lead author of the study and retired professor of Earth Sciences at SOEST. “However, we have learned from this study that hotspots can undergo pulses of melt production. A small pulse created the Midway cluster of now extinct volcanoes and another, much bigger one created Pūhāhonu. This will rewrite the textbooks on how mantle plumes work.”

[…]

University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology

Are We Seeing a New Ocean Starting to Form in Africa?

by Klemetti, E., May 8, 2020 in EOS


Although shallow magma storage at Erta Ale volcano hints at a rift-to-ridge transition, the tectonic future of the Afar region is far from certain.

Standing next to a lava lake at the summit of a massive volcano, Christopher Moore, a Ph.D. candidate at the School of Earth and Environment at the University of Leeds in the United Kingdom, could see the red haze of lava flows a few kilometers away. This might seem like a rare sight, but at Ethiopia’s Erta Ale, it’s business as usual.

Are such behaviors the first signs of a tectonic transition? This question is part of what Moore has been studying at Erta Ale. The entire Afar region in eastern Africa finds itself in the middle of changes that could split the continent, forming a new ocean basin. The magmatism at Erta Ale might be offering signs of this switch by mimicking the characteristics of a mid-ocean ridge.

Satellite image of eastern Africa, with the Red Sea and the Gulf of Aden to the east
The East African Rift valley, the Red Sea, and the Gulf of Aden are clearly visible in this Landsat 8 image, taken on 8 November 2019. Credit: NASA/Erik Klemetti

However, there isn’t agreement about how close the Afar region is to this tectonic transition. The geophysical characteristics of magma storage at Erta Ale could point to the region’s conversion to an incipient oceanic spreading center, but the petrology of the erupting lava might be telling us that we aren’t there yet.

Did heavy rains trigger the eruption of the most dangerous U.S. volcano? Scientists are skeptical

by  RP Ortega, April 22, 2020 in ScienceAAAS


In May 2018, Hawaii’s Kilauea volcano let loose its largest eruption in 200 years, spewing plumes of ash high into the air, and covering hundreds of homes in lava. The eruption terrified local residents, but it gave scientists a once-in-a-lifetime opportunity to study the volcano’s explosive behavior. Now, a new study claims that extreme rainfall boosted underground pressures and was the “dominant factor” in triggering the eruption.

It’s not the first time rainfall has been linked to volcanic activity, says Jenni Barclay, a volcanologist at the University of East Anglia who was not involved in the new work. Previous research suggests storms passing over Mount St. Helens may have played a role in explosive activity between 1989 and 1991. And intense rains fell shortly before and during the activity of Montserrat’s Soufrière Hills volcano from 2001 to 2003. Rain may have also triggered eruptions of Réunion’s Piton de la Fournaise volcano. Still, Barclay believes rain is, at best, a contributing factor to volcanic eruptions and not the main driver. “It’s a series of coincident events that have led to the triggering of this larger episode,” she says.

Researchers on the new study used satellite data from NASA and Japan’s space agency to estimate rainfall during the first months of 2018, before the start of the eruption. More than 2.25 meters of rain fell on the volcano in the first months of 2018, the researchers found. They created a model to show how the accumulated rainfall could seep into the pore spaces in rocks deep underground, boosting pressures that eventually caused fissures in the volcano’s flank to open up and release magma. When they looked at records of previous Kilauea eruptions going back to 1790, they found that 35—more than half—started during the nearly 6-month rainy season.

Lunar Recession and the Age of the Earth: How Uniformitarianism Works

by D. Middleton, March 24, 2020 in WUWT


One of the things I love about writing for Watts Up With That, is the fact that reader comments often inspire me to research and write subsequent posts. In my recent post about the origins of the Moon, one commentator suggested that the rate of lunar recession (tidal acceleration) indicated that the Earth was much younger than 4.5 billion years old and/or somehow disproved the geological Principle of Uniformitarianism. I didn’t give much thought to my reply. I simply calculated the distance from the Earth to the Moon 1 billion and 4.5 billion years ago. The Moon is currently receding (moving away) from the Earth at a rate of about 3.8 cm/yr. This has been directly measured with lasers.

At 3.8 cm/yr, the Moon would have been 215,288 miles away from Earth a billion years ago. It is currently an average of 238,900 miles away. At 3.8 cm/yr, it still would have been 132,646 miles away 4.5 BY.

If the Moon did did originate from a collision with Earth, it would have been a lot closer to Earth 4.5 BY than 100,000 miles.

A chunk of Yellowstone the size of Chicago has been pulsing. Why?

by R.G. Andrews, March 19, 2020 in NationalGeographic


An injection of magma under Norris Geyser Basin may be why the region is five inches higher today than it was 20 years ago.

In northwestern Wyoming, in the center of Yellowstone National Park, a bubbling caldera is the scar of a 640,000-year-old, gargantuan volcanic eruption. The 3,472-square-mile park encompassing the caldera is filled with geologic wonderlands of sprouting geysers and effervescing pools, all ultimately driven by magma and superheated fluids churning in the rock below the surface.

One of these areas, Norris Geyser Basin to the northwest of the caldera, contains more than 500 hydrothermal features. These tempestuous geysers and pools often change from day to day, but a much larger transformation has been taking place as well: For more than two decades, an area larger than Chicago centered near the basin has been inflating and deflating by several inches in erratic bursts. In a hyperactive volcanic region like Yellowstone, the exact causes of any specific movement are difficult to pin down. But a recent study in the Journal of Geophysical Research: Solid Earth may help explain why this pocket of land has been breathing in and out.

“In all likelihood, Norris has been a center of deformation for a very long time,” says Daniel Dzurisin, a research geologist at the U.S. Geological Survey’s Cascades Volcano Observatory and one of the co-authors of the new research.

Norris Geyser Basin, Yellowstone National Park, Wyoming.
PHOTOGRAPH BY MARC MORITSCH, NAT GEO IMAGE COLLECTION

‘Melting rock’ models predict mechanical origins of earthquakes

by Duke University, January 17, 2019 in ScienceDaily/Nature


Engineers at Duke University have devised a model that can predict the early mechanical behaviors and origins of an earthquake in multiple types of rock. The model provides new insights into unobservable phenomena that take place miles beneath the Earth’s surface under incredible pressures and temperatures, and could help researchers better predict earthquakes — or even, at least theoretically, attempt to stop them.

The results appear online on January 17 in the journal Nature Communications.

“Earthquakes originate along fault lines deep underground where extreme conditions can cause chemical reactions and phase transitions that affect the friction between rocks as they move against one another,” said Hadrien Rattez, a research scientist in civil and environmental engineering at Duke. “Our model is the first that can accurately reproduce how the amount of friction decreases as the speed of the rock slippage increases and all of these mechanical phenomena are unleashed.”

For three decades, researchers have built machines to simulate the conditions of a fault by pushing and twisting two discs of rock against one another. These experiments can reach pressures of up to 1450 pounds per square inch and speeds of one meter per second, which is the fastest underground rocks can travel. For a geological reference point, the Pacific tectonic plate moves at about 0.00000000073 meters per second.

Hadrien Rattez, Manolis Veveakis. Weak phases production and heat generation control fault friction during seismic slip. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-019-14252-

Breakthrough gives insight into early complex life on Earth

by H. Devlin, January 15, 2020 in TheGuardian


For the first 2 billion years, life on Earth comprised two microbial kingdoms – bacteria and archaea. They featured an innumerable and diverse variety of species, but, ultimately, life on Earth was not that exciting judged by today’s standards.

Then, the theory goes, a rogue archaeon gobbled up a bacterium to create an entirely new type of cell that would go on to form the basis of all complex life on Earth, from plants to humans.

Now, for the first time, scientists have succeeded in culturing an elusive species of archaea believed to be similar to the ancestor that gave rise to the first sophisticated cells, known as eukaryotes. The work has been described as a “monumental” advance that sheds new light on this evolutionary milestone.

Nick Lane, professor of evolutionary biochemistry at UCL, described the work as “magnificent”, while a commentary by two other experts in the field said it marked a “huge breakthrough for microbiology”.

Like bacteria, archaea continue to thrive on Earth today. But despite the pivotal role they are thought to have played in the emergence of complex life there has been relatively little research on them. Many species are found in inhospitable environments and are incredibly difficult to grow in the lab.

The Japanese team behind the latest advance has dedicated 12 years to the effort, overcoming a series of setbacks along the way.

The archaeon which was cultured and characterised from deep marine sediment. Photograph: Nature

 

800,000 Years Ago, a Meteor Slammed Into Earth. Scientists Just Found the Crater.

by M. Weisberger, January 7, 2020 in LiveScience


About 790,000 years ago, a meteor slammed into Earth with such force that the explosion blanketed about 10% of the planet with shiny black lumps of rocky debris. Known as tektites, these glassy blobs of melted terrestrial rock were strewn from Indochina to eastern Antarctica and from the Indian Ocean to the western Pacific. For more than a century, scientists searched for evidence of the impact that created these pitted blobs.

But the crater’s location eluded detection — until now.

Geochemical analysis and local gravity readings told researchers that the crater lay in southern Laos on the Bolaven Plateau; the ancient impact was concealed under a field of cooled volcanic lava spanning nearly 2,000 square miles (5,000 square kilometers), the scientists reported in a new study.

Was the crater buried? On Laos’ Bolaven Plateau, the scientists found a site where fields of volcanic lava might have hidden signs of an older meteor impact. In a region that the researchers targeted as a likely spot for a crater, most of the lava flows were also in the right age range: between 51,000 and 780,000 years old.

In this geological map of the volcanic field’s summit region, the dashed, yellow ellipse marks the buried crater perimeter for the best-fitting gravity model. The dashed, white circle marks the buried perimeter that best fits geological observations. (Image credit: Sieh et al./PNAS 2019)

The study authors peered below the lava’s surface by taking gravity readings at more than 400 locations. Their resulting gravity map showed one area “of particular interest” with a gravitational anomaly, a subsurface zone less dense than the volcanic rock surrounding it. Their measurements hinted at an elliptical, “elongated crater” about 300 feet (100 m) thick, about 8 miles (13 km) wide and 11 miles (17 km) long, according to the study.

Together, all of these clues suggested that “this thick pile of volcanic rocks does indeed bury the site of the impact,” the scientists wrote.

The findings were published online Dec. 30 in the journal Proceedings of the National Academy of Sciences.

Big volcanic bump unlike anything seen before found on the moon

by R.G. Andrews, December 13, 2019 in NationalGeography


Scientists scouring the lunar surface for clues to past impact rates found a bonus feature that has geologists “thoroughly confused.”

Sometime after the solar system formed 4.6 billion years ago, a projectile slammed into Earth’s youthful moon and formed the 620-mile-wide basin known as the Crisium basin. No one knows exactly when this impact happened, but for decades scientists have been trying to solve the puzzle as part of a larger debate over whether the moon and, by proxy, Earth endured a period of frenzied meteor bombardment in their early histories.

Now, scientists scouring the region say they’ve spotted a crater within the basin that appears to contain pristine impact melt, a type of volcanic rock that can act like a definitive geologic clock. If future astronauts or a robot could obtain a sample and tease out its age, that may help reveal what was happening on Earth during the primordial period when life first emerged on our planet.

And, as an added bonus, the discovery comes with an intriguing mystery: The basin also holds a geologic blister the size of Washington, D.C., that’s unlike anything else seen in the solar system. As the team reports in an upcoming paper in the Journal of Geophysical Research: Planets, this volcanic lump appears to have been inflated and cracked by peculiar underground magmatic activity that the researchers can’t currently explain.

“I’m thoroughly confused by it,” says Clive Neal, an expert in lunar geology at the University of Notre Dame who was not involved with the new research.

 

Le Précambrien : les bactéries, la tectonique des plaques et l’oxygène (2/2)

by Alain Préat, 25 septembre 2019 in Science-Climat-Energie


Résumé : L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète (nb: première partie 1/2, ici).

Malgré un apport en oxygène lié aux cyanobactéries dès l’Archéen, ce ne se sont pas ces microorganismes qui sont à la base de la première grande ‘révolution’ de l’oxygène qui a eu lieu à la limite Archéen/Paléoprotérozoïque (il y a 2,5 milliards d’années) dans l’atmosphère, lors du Grand Evénement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique vers 2,5 milliards d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite (= FeS2). L’altération des séries riches en ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’Archéen sera remplacée par une atmosphère oxydante à la fin du Précambrien.

Abstract : Oxygen did not appear as abruptly as we thought on our planet.

Despite an oxygen supply related to cyanobacteria, since the Archean, it is not these microorganisms that are at the base of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (2.5 billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the of atmospheric oxygen concentration 2.5 billion years ago. These two main processes are related to the burial of organic matter and those of pyrite(= FeS2) The alteration of series with high contents of the two elements will then condition for nearly a billion of years the oxygen, sulfur and iron chemical composition of the oceans. The oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian.

Le Précambrien : les bactéries, la tectonique des plaques et l’oxygène (1/2)

by Alain Préat, 20 septembre 2019, in ScienceClimatEnergie


Résumé : L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète.

Malgré un apport en oxygène lié aux cyanobactéries dès l’Archéen, ce ne se sont pas ces micro-organismes qui sont à la base de la première grande ‘révolution’ de l’oxygène qui a eu lieu à la limite Archéen/Paléoprotérozoïque (il y a 2,5 milliards d’années) dans l’atmosphère, lors du Grand Evénement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique vers 2,5 milliards d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite (= FeS2). L’altération des séries riches en ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’Archéen sera remplacée par une atmosphère oxydante à la fin du Précambrien.

Abstract : Oxygen did not appear as abruptly as we thought on our planet.

Despite an oxygen supply related to cyanobacteria, since the Archean, it is not these microorganisms that are at the base of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (2.5 billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the of atmospheric oxygen concentration 2.5 billion years ago. These two main processes are related to the burial of organic matter and those of pyrite (= FeS2). The alteration of series with high contents of the two elements will then condition for nearly a billion of years the oxygen, sulfur and iron chemical composition of the oceans. The oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian.

OLYMPUS DIGITAL CAMERA

Figure 2a( en haut). Stromatolithe columnaire, Néoprotérozoïque, (Formation SC1c in Préat et al. 2018), Bassin du Niari, République du Congo (Brazzaville), photo A. Préat, 2016.

Oxygen depletion in ancient oceans caused major mass extinction

by Florida State University, August. 30, 2019 in ScienceDaily/fromGeology


Late in the prehistoric Silurian Period, around 420 million years ago, a devastating mass extinction event wiped 23 percent of all marine animals from the face of the planet.

For years, scientists struggled to connect a mechanism to this mass extinction, one of the 10 most dramatic ever recorded in Earth’s history. Now, researchers from Florida State University have confirmed that this event, referred to by scientists as the Lau/Kozlowskii extinction, was triggered by an all-too-familiar culprit: rapid and widespread depletion of oxygen in the global oceans.

Deducing the scale of tsunamis from the ’roundness’ of deposited gravel

by Tokyo Metropolitan University, August 25, 2019 in ScienceDaily


Scientists from Tokyo Metropolitan University and Ritsumeikan University have found a link between the “roundness” distribution of tsunami deposits and how far tsunamis reach inland. They sampled the “roundness” of gravel from different tsunamis in Koyadori, Japan, and found a common, abrupt change in composition approximately 40% of the “inundation distance” from the shoreline, regardless of tsunami magnitude. Estimates of ancient tsunami size from geological deposits may help inform effective disaster mitigation.

Journal Reference: Daisuke Ishimura, Keitaro Yamada. Palaeo-tsunami inundation distances deduced from roundness of gravel particles in tsunami deposits. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-019-46584-z

A voracious Cambrian predator, Cambroraster, is a new species from the Burgess Shale

by Royal Ontario Museum, July 31, 2019 in ScienceDaily


Fossils of a large new predatory species in half-a-billion-year-old rocks have been uncovered from Kootenay National Park in the Canadian Rockies. This new species has rake-like claws and a pineapple-slice-shaped mouth at the front of an enormous head, and it sheds light on the diversity of the earliest relatives of insects, crabs, spiders, and their kin.

Reaching up to a foot in length, the new species, named Cambroraster falcatus, comes from the famous 506-million-year-old Burgess Shale. “Its size would have been even more impressive at the time it was alive, as most animals living during the Cambrian Period were smaller than your little finger,” said Joe Moysiuk, a graduate student based at the Royal Ontario Museum who led the study as part of his PhD research in Ecology & Evolutionary Biology at the University of Toronto. Cambroraster was a distant cousin of the iconic Anomalocaris, the top predator living in the seas at that time, but it seems to have been feeding in a radically different way,” continued Moysiuk.

Rare fossil in a fossil reveals a dinosaur’s surprising last meal

by Michael Gresko, July 11, 2019 in NationalGeographic


The find—described today in the journal Current Biology—is the fourth Microraptor fossil to preserve stomach contents, but it’s the first to show that Microraptor ate lizards. Previous fossils captured it eating small mammals, fish, or birds. The specimen also reveals that, like some predatory birds today, Microraptor had a taste for swallowing lizards whole and head-first.

This fossil of the feathered dinosaur Microraptor also preserves the animal’s last meal: a lizard it seems to have swallowed whole and head first.

PHOTOGRAPH BY XUWEI YIN

Antarctic marine life recovery following the dinosaurs’ extinction

by British Antarctic Survey, June 19, 2019 in ScienceDaily


The K-Pg extinction wiped out around 60% of the marine species around Antarctica, and 75% of species around the world. Victims of the extinction included the dinosaurs and the ammonites. It was caused by the impact of a 10 km asteroid on the Yucatán Peninsula, Mexico, and occurred during a time period when the Earth was experiencing environmental instability from a major volcanic episode. Rapid climate change, global darkness, and the collapse of food chains affected life all over the globe.

The K-Pg extinction fundamentally changed the evolutionary history of life on Earth. Most groups of animals that dominate modern ecosystems today, such as mammals, can trace the roots of their current success back to the aftermath of this extinction event.

A team of scientists from British Antarctic Survey, the University of New Mexico and the Geological Survey of Denmark & Greenland show that in Antarctica, for over 320,000 years after the extinction, only burrowing clams and snails dominated the Antarctic sea floor environment. It then took up to one million years for the number of species to recover to pre-extinction levels.