by Alain Préat, 31 mai 2018, Académie Royale des Sciences d’Outre- Mer
Le Précambrien représente 88% de l’histoire de la Terre âgée de 4,567 milliards d’années (Ga).
C’est au cours de cette période peu connue, peu enseignée que se sont déroulés ou mis en place des événements physico-chimiques et biologiques déterminants: différenciation des enveloppes terrestres, tectonique des plaques et premières ‘pangées’ ou supercontinents, champ magnétique, chaînes de montagnes, glaciations, anoxies des bassins, remplacement du CO2-CH4par l’oxygène atmosphérique, formation de gisements (uranium, manganèse, nickel …. et même pétrole), émergence dès 3,8 Ga des procaryotes puis des eucaryotes …
Vu l’absence de fossiles stratigraphiques, et donc de biozones, la stratigraphie du Précambrien est encore très difficile, elle est intialement basée sur la lithostratigraphie. De grands progrès ont récemment été réalisés grâce à la chimiostratigraphie istotopique (C, O, Sr….) en plus de la radiométrie absolue.
L’exposé se consacrera aux événements sédimentaires liés au Grand Evénement de l’Oxygène il y a environ 2,5-2,1 Ga (Paléoprotérozoïque) et à ceux liés à la ‘Terre Boule de Neige’ (Snowball Earth) avec la glaciation marinoenne il y a 0,635 Ga (Néoprotérozoïque), à partir des séries de l’Afrique de l’Ouest.
By Field Museum, May 24, 2018 in ScienceDaily (CurrentBiology)
Sixty-six million years ago, the world burned. An asteroid crashed to Earth with a force one million times larger than the largest atomic bomb, causing the extinction of the dinosaurs. But dinosaurs weren’t the only ones that got hit hard — in a new study, scientists learned that the planet’s forests were decimated, leading to the extinction of tree-dwelling birds.
by Rice University, May 16, 2018 in ScienceDaily
Clues from some unusual Arizona rocks pointed Rice University scientists toward a discovery — a subtle chemical signature in rocks the world over — that could answer a long-standing mystery: What stole the iron from Earth’s continents?
The find has weighty implications. If the iron content of continental rocks was a bit greater, as it is in the rocks beneath Earth’s oceans, for example, our atmosphere might look more like that of Mars, a planet so littered with rusty, oxidized rocks that it appears red even from Earth.
In a new paper available online in Science Advances, Rice petrologists Cin-Ty Lee, Ming Tang, Monica Erdman and Graham Eldridge make a case that garnet steals the most iron from continents. The hypothesis flies in the face of 40-plus years of geophysical thinking, and Tang, a postdoctoral fellow, and Lee, professor and chair of the Department of Earth, Environmental and Planetary Sciences at Rice, said they expect a healthy dose of skepticism from peers.
“The standard view … (…)
by Geological Society of America, May 3, 2018 in ScienceDaily
Over the last 5000 years, Mount Taranaki volcano, located in the westernmost part of New Zealand’s North Island, produced at least 16 Plinian-scale explosive eruptions, the latest at AD 1655. These eruptions had magnitudes of 4 to 5, eruptive styles, and contrasting basaltic to andesitic chemical compositions comparable to the eruptions of Etna, 122 BC; Vesuvius, AD79; Tarawera, 1886; Pelée, 1902; Colima, 1910; Mount Saint Helens, 1980; Merapi, 2010; and Calbuco, 2015.
by GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre, May 1, 2018 in ScienceDaily
The metropolitan area of Istanbul with around 15 million inhabitants is considered to be particularly earthquake-prone. In order to be able to assess the risk correctly, researchers must decipher the processes underground. Below the Marmara Sea, an international research team detected earthquakes that were not directly caused by tectonic stresses but by rising natural gas.
by Geological Society of America and in Geology, April 19,2018 in ScienceDaily
.pdf of the article
In early 2017 scientists announced the discovery of possible desiccation cracks in Gale Crater, which was filled by lakes 3.5 billion years ago. Now, a new study has confirmed that these features are indeed desiccation cracks, and reveals fresh details about Mars’ ancient climate.
“We are now confident that these are mudcracks,” explains lead author Nathaniel Stein, a geologist at the California Institute of Technology in Pasadena. Since desiccation mudcracks form only where wet sediment is exposed to air, their position closer to the center of the ancient lake bed rather than the edge also suggests that lake levels rose and fell dramatically over time.
by Arizona State University, April 17, 2018 in ScienceDaily
About 252 million years ago, more than 90 percent of all animal life on Earth went extinct. This event, called the “Permian-Triassic mass extinction,” represents the greatest catastrophe in the history of life on Earth. Ecosystems took nearly five million years to recover and many aspects of the event remain a mystery.
A research team, led by scientists from Arizona State University and funded by NASA and the National Science Foundation, is helping to understand why this extinction event happened and why it took life so long to recover. The study, published in Science Advances, was led by ASU School of Earth and Space Exploration graduate student Feifei Zhang, with direction from school faculty member Ariel Anbar.
by Michigan State University, April 3, 2018 in Sciencedaily
Scientists now have a clearer picture of the Earth’s mantle, thanks to Michigan State University research published in the current issue of Nature Communications (…)
by Simon Fraser University, March 29,2018 in ScienceDaily
A new 53 million-year-old insect fossil called a scorpionfly discovered at B.C.’s McAbee fossil bed site bears a striking resemblance to fossils of the same age from Pacific-coastal Russia, giving further evidence of an ancient Canada-Russia connection.
by U. of California – Santa Barbara, March 29, 2018 in SciencedDaily
To borrow from a philosophical thought experiment: If a volcano erupts in a remote part of the world and no one hears it, does it still make a sound?
Indeed, it does. And not only does the sound occur, but it also can tell scientists about the timing and duration of the eruption itself (…)
by D.C. McLaren et al., 2018 in PLOS.ONE
Little is known about the ice age human occupation of the Pacific Coast of Canada. Here we present the results of a targeted investigation of a late Pleistocene shoreline on Calvert Island, British Columbia. Drawing upon existing geomorphic information that sea level in the area was 2–3 m lower than present between 14,000 and 11,000 years ago, we began a systematic search for archaeological remains dating to this time period beneath intertidal beach sediments (…)
by F. Guldstrand et al., 2018 in Front.Earth.Sci.
• We quantitatively analyse pre-eruptive intrusion-induced surface deformation from 33 scaled laboratory experiments resulting in eruptions.
• A robust proxy extracted from surface deformation geometry enables systematic predictions of the locations of a subsurface intrusion and imminent eruption.
• Forecasting an eruption location is possible without geodetic modeling but requires volcano monitoring at high spatiotemporal resolution.
by University of California-Berkeley, March 19, 2018 in ScienceDaily
A new theory about how oceans and volcanoes interacted during the early history of Mars supports the idea that liquid water was once abundant and may still exist underground. Geophysicists propose that the oceans originated several hundred million years earlier than thought, as the volcanic province Tharsis formed, and that greenhouse gases enabled the oceans. The theory predicts smaller oceans, more in line with estimates of water underground and at the poles today.
by University of Cap Town, March 12, 2018 in ScienceDaily
Early modern humans living in South Africa around 74,000 years ago prospered through the cataclysmic eruption of the Toba supervolcano in Sumatra. The Toba eruption was one of the Earth’s most explosive volcanic events. The environmental effects of this event have been heavily debated, with some researchers having previously proposed that the eruption led to a worldwide volcanic winter that devastated contemporaneous human populations.
An eruption a hundred times smaller than Mount Toba — that of Mount Tambora, also in Indonesia, in 1815 — is thought to have been responsible for a year without summer in 1816. The impact on the human population was dire — crop failures in Eurasia and North America, famine and mass migrations. The effect of Mount Toba, a super-volcano that dwarfs even the massive Yellowstone eruptions of the deeper past, would have had a much larger, and longer-felt, impact on people around the globe (…)
by University of Nevada, March 9, 2018 in ScienceDaily
A UNLV scientist has discovered the first direct evidence that fluid water pockets may exist as far as 500 miles deep into the Earth’s mantle.
Groundbreaking research by UNLV geoscientist Oliver Tschauner and colleagues found diamonds pushed up from the Earth’s interior had traces of unique crystallized water called Ice-VII.
See alos here