Axial precession of Earth

Rotation Speed and Axial Tilts of the Planets in Our Solar System

 

Dr. James O’Donoghue, a Planetary at NASA Goddard created a brilliant animation of the planets in our solar system. Using NASA imagery for each planet, O’Donoghue plotted the exact rotation periods (in hours and days) and the angle at which they rotate (axial tilt).

"Oceanic Rainforest" - Why and How we need to save them?

  Saving the Rainforest of the Ocean

--Arindam Biswas

A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Sometimes called rainforests of the sea, shallow coral reefs form some of Earth's most diverse ecosystems. They are fragile, partly because they are sensitive to water conditions. There are uplifted reefs also and they form a kind of marine terrace found in intertropical regions as a result of biological activity, shoreline advance and accumulation of reef materials. The formation of these platforms is controlled by changes in environmental conditions and by tectonic activity during recent geological times. Changes in climatic conditions have led to eustatic sea-level oscillations and isostatic movements of the Earth's crust, especially with the changes between glacial and interglacial periods.

Source: Hello Travel

Topographic and hydrographic information are basic elements in studies of nearshore geomorphology, hydrology, and sedimentary processes. This information includes both longterm and short-term changes taking place along the coast; which includes beach profiles, and changes due to erosion (Klemas, 2009). Remote sensing from satellites is an efficient and cost-effective approach to carry out the study. While remote sensing cannot provide the level of detail and accuracy at a single point than a field survey, the statistical power for inferring large scale patterns benefits in having complete areal coverage. Remote sensing imagery in the visible wavelengths is commonly used to perform mapping on coral reefs, utilising multispectral and hyperspectral data, acquired by airborne or satellite-based sensors. Both spatial and spectral resolutions help discriminate various mapping objective, from geomorphic zones (e.g., fore reef, reef crest) to benthic community cover (e.g., coral on reef matrix, algae and coral on rubble).  

Remote sensing covers many technologies, from satellites to airborne sensors, unmanned aerial systems, boat-based systems, and autonomous underwater vehicles. Using available remote sensing technologies for coral reef mapping, the extent of the reef can be studied routinely. Apart from mapping only, the rugosity, macroalgal matters, and bleached corals present in the colony can also be studied.  

A fire coral before (left) and after (right) bleaching. (Source: Mongabay)

Remote sensing techniques are also used to identify the proxy for various environmental parameters, such as estimation of water attenuation as a proxy for water depth, turbidity for sedimentation, algal bloom for pollution, and sea surface temperature for thermal stress....... To read the full story click here.

How Earth is retaining its magnetic field?

Image Source: Today I Found Out

First of all, the Earth shows it's magnetic field because of it's internal geodynamic nature. And it is believed that Earth's outer core is responsible for this kind of behavior. Unlike the mineral-rich crust and mantle, the core is made almost entirely of metals. Along with iron (Fe), silicon (Si) is also found at Earth’s core whose thermal conductivity has an impact on Earth’s thermal structure, evolution, and dynamics, as it controls the magnitude of thermal and compositional sources required to sustain the internal geodynamo of Earth. Scientists have directly measured the thermal conductivity of both solid Fe and Fe-Si alloys up to 144 GPa and 3300 K. 15 at% Si alloyed in Fe significantly reduces its conductivity by almost 2 folds at 132GPa and 3000 K. At similar pressure-temperature conditions, an outer core with 15 at% Si would have a conductivity of about 20 W m^-1 K^-1, which is lower than pure Fe. This suggests that a lower minimum heat flow, around 3TW, across the core-mantle boundary than previously expected, and thus less thermal energy needed to operate the geodynamo.

🔖 To know more about this research Click here.

Earth's Plate Tectonics Began Over 3.2 Billion Years Ago

Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga

by  Alec R. Brenner et al.

An artistic cross-section through forming Earth's crust approximately 3-4 billion years ago. Image credit: Alec R. Brenner

Plate tectonics has been the dominant surface geodynamical regime throughout Earth’s recent geological history. One defining feature of modern plate tectonics is the differential horizontal motion of rigid lithospheric plates. The physiography and composition of Earth’s modern crust bear evidence for plate tectonic or “mobile-lid” processes including subduction, collisional orogeny, rifting, and ocean spreading. The case for the Archean Earth [4.0 to 2.5 billion years (Ga) ago] is not so clear. The surviving Archean crust consists of ~35 cratons, most with characteristic architecture of rounded granitoid intrusive domes rimmed by steeply dipping greenstone keels. The composition of extant Archean crust is substantially more mafic than modern oceanic crust, with a high fraction of ultramafic rocks such as komatiites. These structural and compositional differences have led to a number of proposals that the Archean crust was constructed by exotic processes, including plume tectonics, sagduction/drip tectonics, and a vertically overturning lithosphere. Since some of these processes are difficult to reconcile with plate mobility, alternative geodynamical regimes have been proposed for the Archean Earth, including stagnant-lid and sluggish-lid modes in which the lithosphere was rendered immobile, or at least slowed, due to decoupling from the asthenosphere under elevated geothermal gradients. Other studies argue for a uniformitarian model of the Archean Earth, in which some variant of modern plate tectonics was in operation at least locally throughout Earth history. Complete understanding of the Archean lithosphere, hydrosphere, atmosphere, and biosphere are predicated upon distinguishing between these proposed Archean geodynamic modes. Insights into these components of the early Earth are foundational to the inner workings of terrestrial planets generally and what surface conditions and environments hosted the development of the first life.

Arguments for alternative geodynamical regimes in the Archean are often based on inferences of a regime transition toward modern-style plate tectonics. Existing estimates for the age of such a transition range from the Neoproterozoic to the Hadean (see the Supplementary Materials) and invoke a range of observations including global and local geochemical records, field relations of possible syn-tectonic rocks, and paleomagnetic pole comparisons.  

A key discriminant between stagnant- and mobile-lid regimes is the rate of horizontal motion of plates over Earth’s surface. Absolute plate velocities have typically been ~2 to 10 cm/year (extremes from 0 to 25 cm/year) over the last 400 million years (Ma), while hypothesized velocities for stagnant- and sluggish-lid models are typically less than 2 cm/year. Paleomagnetic methods may constrain the velocity of crustal blocks in deep geological time by measuring their apparent polar wander histories. However, robust paleomagnetic evidence for latitudinal motion has been lacking thus far for times before 2.8 Ga. Here, we produce a new paleomagnetic pole from ~3180 Ma volcanics in the East Pilbara Craton of Western Australia and use this result to assess the presence of plate tectonic– like processes on Earth before that time.  

Original article: Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga. DOI: 10.1126/sciadv.aaz8670. To read the article click here.

Earth’s oldest recognized meteorite impact structure

Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure (Research work by Erickson et al.)

Composite aeromagnetic anomaly map of the Yarrabubba impact structure within the Yilgarn Craton, Western Australia, showing the locations of key outcrops and samples used in this study. The image combines the total magnetic intensity (TMI, cool to warm colours) with the second vertical derivative of the total magnetic intensity (2VD, grayscale) data. The demagnetized anomaly centred on the outcrops of the Barlangi granophyre is considered to be the eroded remnant of the central uplift domain, which forms the basis of the crater diameter of 70 km. Prominent, narrow linear anomalies that cross-cut the demagnetized zone with broadly east-west orientations are mafic dykes that post-date the impact structure.  

The ~70 km-diameter Yarrabubba impact structure in Western Australia is regarded as among Earth’s oldest but has hitherto lacked precise age constraints. Here we present U–Pb ages for impact-driven shock-recrystallised accessory minerals. Shock-recrystallised monazite yields a precise impact age of 2229 ± 5 Ma, coeval with shock-reset zircon. This result establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth, extending the terrestrial cratering record back >200 million years. The age of Yarrabubba coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits, the Rietfontein diamictite in South Africa. Numerical impact simulations indicate that a 70 km diameter crater into a continental glacier could release between 8.7 × 1013 to 5.0 × 1015 kg of H2O vapour instantaneously into the atmosphere. These results provide new estimates of impact-produced H2O vapour abundances for models investigating termination of the Paleoproterozoic glaciations and highlight the possible role of impact cratering in modifying Earth’s climate. The ~70 km-diameter Yarrabubba impact structure in Western Australia has previously been regarded as among Earth’s oldest meteorite craters but has hitherto lacked absolute age constraints. Here, the authors determine a precise impact age of 2229 ± 5 Ma, which extends the terrestrial cratering record back in time by > 200 million years and establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth.

Original article: Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest

recognised meteorite impact structure. DOI:  10.1038/s41467-019-13985-7. To read the article click here.

By 2025, carbon dioxide levels in Earth’s atmosphere will be higher than at any time in the last 3.3 million years

By 2025, carbon dioxide levels in Earth’s atmosphere will be higher than at any time in the last 3.3 million years

Source: GeologyPage

The composition of fossilised zooplankton shells has enabled the
reconstruction of past pH and CO2. Credit: University of Southampton  

By 2025, atmospheric carbon dioxide (CO2) levels will very likely be higher than they were during the warmest period of the last 3.3 million years, according to new research by a team from the University of Southampton published today in Nature Scientific Reports.

The team studied the chemical composition of tiny fossils, about the size of a pinhead collected from the deep ocean sediments of the Caribbean Sea. They used this data to reconstruct the concentration of CO2 in Earth’s atmosphere during the Pliocene epoch, around 3 million years ago when our planet was more than 3°C warmer than today with smaller polar ice caps and higher global sea-levels.

 

Dr. Elwyn de la Vega, who led the study, said: “Knowledge of CO2 during the geological past is of great interest because it tells us how the climate system, ice sheets and sea-level previously responded to the elevated CO2 levels. We studied this particular interval in unprecedented detail because it provides great contextual information for our current climate state.”

To determine atmospheric CO2, the team has used the isotopic composition of the element boron, naturally present as an impurity in the shells of zooplankton called foraminifera or ‘forams’ for short. These organisms are around half a millimetre in size and gradually accumulate in huge quantities on the seabed, forming a treasure trove of information on Earth’s past climate. The isotopic composition of the boron in their shells is dependent on the acidity (the pH) of the seawater in which the forams lived. There is a close relationship between atmospheric CO2 and seawater pH, meaning past CO2 can be calculated from the careful measurement of the boron in ancient shells.

 

Dr. Thomas Chalk, a co-author of the study, added: “Focussing on a past warm interval when the incoming insolation from the Sun was the same as today gives us a way to study how Earth responds to CO2 forcing. A striking result we’ve found is that the warmest part of the Pliocene had between 380 and 420 parts per million CO2 in the atmosphere. This is similar to today’s value of around 415 parts per million, showing that we are already at levels that in the past were associated with temperature and sea-level were significantly higher than today. Currently, our CO2 levels are rising at about 2.5 ppm per year,  meaning that by 2025 we will have exceeded anything seen in the last 3.3 million years.”

Professor Gavin Foster, who was also involved in the study, continued: “The reason we don’t see Pliocene-like temperatures and sea-levels yet today is that it takes a while for Earth’s climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium.”

Concluded Dr. de la Vega, “Having surpassed Pliocene levels of CO2 by 2025, future levels of CO2 are not likely to have been experienced on Earth at any time for the last 15 million years, since the Middle Miocene Climatic Optimum, a time of even greater warmth than the Pliocene.”

Original article: The paper, “Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation” is published in Nature Scientific Reports. DOI: 10.1038/s41598-020-67154-8

NASA Monitors Environmental Signals From Global Response to COVID-19

NASA Monitors Environmental Signals From Global Response to COVID-19

Source: NASA

Decreases in air pollution, specifically tropospheric nitrogen dioxide (NO2), over the Northeast United States due to COVID-19 response. Credits: NASA / Science Visualization Studio.

For the past several weeks, much of the world has experienced a new normal: one with fewer cars on the road and more time spent at home. Despite these changes, NASA’s Earth-observing fleet continues to operate, collecting key observations on how the planet is responding to this changing behaviour due to restrictions in place from COVID-19.

“Much like our satellites, our work continues remotely,” explains Acting Director for NASA’s Earth Science Division Sandra Cauffman. “NASA Earth scientists continue to collect and analyze satellite and ground-based data on a global scale, and our programs are helping to characterize and understand the global environmental signals. We do this by analyzing existing, long-term datasets and funding new, cutting-edge research.”

Ongoing observations of air quality and of Earth at night have helped provide immediate examples of how Earth’s systems are responding to these changes in human behaviour. From space, NASA’s Ozone Monitoring Instrument (OMI) aboard the Aura satellite and the European Space Agency’s TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5P satellite have provided the data behind the images of rapidly falling nitrogen dioxide (NO ) levels around the world due to people sheltering in place.....Read more.