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.
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.
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.
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.
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
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.
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.
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.
A team of scientists have given a fresh insight into what may have driven the “Cambrian Explosion” — a period of rapid expansion of different forms of animal life that occurred over 500 million years ago.
While a number of theories have been put forward to explain this landmark period, the most credible is that it was fuelled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.
The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics.
During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism — chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.
This, the team calculated, led to an increase in atmospheric CO2and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.
One researcher at the University of Tokyo is in hot pursuit of dinosaurs, tracking extinct species around ancient Earth. Identifying the movements of extinct species from millions of years ago can provide insights into ancient migration routes, interaction between species, and the movement of continents.
“If we find fossils on different continents from closely related species, then we can guess that at some point there must have been a connection between those continents,” said Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo.
A map of life – biogeography
Previous studies in biogeography — the geographic distribution of plants and animals — had not considered the evolutionary relationships between ancient species. The new method that Kubo designed, called biogeographical network analysis, converts evolutionary relationships into geographical relationships.
By combining data from fossils and models of the ancient Earth, researchers can map where ancient species may have migrated. This method, called biogeographical network analysis, converts evolutionary relationships between species into geographical relationships. This method was used in research by Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo. Credit Caitlin Devor, The University of Tokyo, CC-BY Usage Restrictions Image by Caitlin Devor, The University of Tokyo, CC-BY
Last week, Marc Chaussidon, director of the Institute of Geophysics in Paris (IPGP), looked at seafloor maps from a recently concluded mission and saw a new mountain. Rising from the Indian Ocean floor between Africa and Madagascar was a giant edifice 800 meters high and 5 kilometers across. In previous maps, there had been nothing. “This thing was built from zero in 6 months!” Chaussidon says.
His team, along with scientists from the French national research agency CNRS and other institutes, had witnessed the birth of a mysterious submarine volcano, the largest such underwater event ever witnessed. “We have never seen anything like this,” says IPGP’s Nathalie Feuillet, leader of an expedition to the site by the research vessel Marion Dufresne, which released its initial results last week.
The quarter-million people living on the French island of Mayotte in the Comoros archipelago knew for months that something was happening. From the middle of last year they felt small earthquakes almost daily, says Laure Fallou, a sociologist with the European-Mediterranean Seismological Centre in Bruyères-le-Châtel, France. People “needed information,” she says. “They were getting very stressed, and were losing sleep.”
Mercury found in ancient rock around the world supports theory that eruptions caused ‘Great Dying’ 252 million years ago.
Researchers say mercury buried in ancient rock provides the strongest evidence yet that volcanoes caused the biggest mass extinction in the history of the Earth.
The extinction 252 million years ago was so dramatic and widespread that scientists call it “the Great Dying.” The catastrophe killed off more than 95 percent of life on Earth over the course of hundreds of thousands of years.
Paleontologists with the University of Cincinnati and the China University of Geosciences said they found a spike in mercury in the geologic record at nearly a dozen sites around the world, which provides persuasive evidence that volcanic eruptions were to blame for this global cataclysm.
The study was published this month in the journal Nature Communications.
The eruptions ignited vast deposits of coal, releasing mercury vapor high into the atmosphere. Eventually, it rained down into the marine sediment around the planet, creating an elemental signature of a catastrophe that would herald the age of dinosaurs.
“Volcanic activities, including emissions of volcanic gases and combustion of organic matter, released abundant mercury to the surface of the Earth,” said lead author Jun Shen, an associate professor at the China University of Geosciences.
One of the central mysteries of paleontology is the so-called “three-metre problem.” In a century and a half of assiduous searching, almost no dinosaur remains have been found in the layers three metres, or about nine feet, below the KT boundary, a depth representing many thousands of years. Consequently, numerous paleontologists have argued that the dinosaurs were on the way to extinction long before the asteroid struck, owing perhaps to the volcanic eruptions and climate change. Other scientists have countered that the three-metre problem merely reflects how hard it is to find fossils. Sooner or later, they’ve contended, a scientist will discover dinosaurs much closer to the moment of destruction.
Locked in the KT boundary are the answers to our questions about one of the most significant events in the history of life on the planet. If one looks at the Earth as a kind of living organism, as many biologists do, you could say that it was shot by a bullet and almost died. Deciphering what happened on the day of destruction is crucial not only to solving the three-metre problem but also to explaining our own genesis as a species.
Paleontologists have found a fossil site in North Dakota that contains animals and plants killed and buried within an hour of the meteor impact that killed the dinosaurs 66 million years ago. This is the richest K-T boundary site ever found, incorporating insects, fish, mammals, dinosaurs and plants living at the end of the Cretaceous, mixed with tektites and rock created and scattered by the impact. The find shows that dinosaurs survived until the impact.
Based on new data published today in the journal Science, it seems increasingly likely that an asteroid or comet impact 66 million years ago reignited massive volcanic eruptions in India, half a world away from the impact site in the Caribbean Sea.
But it leaves unclear to what degree the two catastrophes contributed to the near-simultaneous mass extinction that killed off the dinosaurs and many other forms of life.
The research sheds light on huge lava flows that have erupted periodically over Earth’s history, and how they have affected the atmosphere and altered the course of life on the planet.
“The Anthropocene as a geological epoch is not formally recognized”… So… “The term Anthropocene has” NOT “been widely used for the current period in Earth’s geological history“. It may be frequently used by activists and scientists who are ignorant of basic geology, but geologically speaking the term “Anthropocene” does not exist in any relationship to any period, epoch, age, era or eon in Earth’s geological history.
Yes, we have no Anthropocene, we have no Anthropocene today… Sung to the tune of Yes, We Have No Bananas.
Explaining the color of rocks is still a complex problem. This question was raised long ago in the community of geologists, particularly for the pigmentation of the ‘red marbles’ of the Frasnian of Belgium at the beginning of the last century, with many unsatisfactory hypotheses. Our recent analysis of different red carbonate rocks in Europe and North Africa (Morocco) may provide an alternative explanation for the color of these rocks. For this it was necessary to bring together diverse and complementary skills involving geologists, microbiologists and chemists. We present here a synthesis of these works. It is suggested that the red pigmentation of our studied Phanerozoic carbonate rocks, encompassing a time range from Pragian to Oxfordian, may be related to the activity of iron bacteria living in microaerophilic environments. A major conclusion is that this red color is only related to particular microenvironments and has no paleogeographic or climatic significance. All red carbonates have not necessarily acquired their pigmentation through the process established in this review. Each geological series must be analyzed in the light of a possible contribution of iron bacteria and Fungi.
Cet article est le résultat d’une recherche multi-disciplinaire entre géologues et biologistes. Une synthèse de cette recherche vient d’être publiée en décembre 2018 sur le site de Geologica Belgica. Un article déjà publié dans SCE peut également être consulté.
Contrairement à ce que l’on peut penser, une question simple nécessite parfois des années de recherches avec des équipes diverses et des moyens sophistiqués. La question simple concerne ici la géologie et plus particulièrement la couleur des roches sédimentaires.
Scientists have described a fossil plant species that suggests flowers bloomed in the Early Jurassic, more than 174 million years ago, according to new research in the open-access journal eLife.
Before now, angiosperms (flowering plants) were thought to have a history of no more than 130 million years. The discovery of the novel flower species, which the study authors named Nanjinganthus dendrostyla, throws widely accepted theories of plant evolution into question, by suggesting that they existed around 50 million years earlier. Nanjinganthus also has a variety of ‘unexpected’ characteristics according to almost all of these theories.
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.
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.
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?
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.
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.
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.”
La géologie, une science plus que passionnante … et diverse