Category: Science

Sahara desert may be older than previously thought

Leave a comment

New findings of climatologists published in Nature reveal that the formation of the Sahara desert may have started up to 7 million years ago, more than twice as long ago as previously thought. Following the discovery of aeolian dune deposits that challenged the widely accepted age of approximately 2 – 3 million years for the Sahara desert, the scientists have used climate models to simulate the mechanisms behind the onset of aridification in northern Africa. Their results show that the origination of the Sahara desert may be related to shrinking of the Tethys Sea and the uplift of the Arabian Peninsula, associated with the northward movement of the African tectonic plate towards the Eurasian tectonic plate during the late Miocene. This reorganization of landmasses is thought to have significantly weakened the African summer monsoon, resulting in a reduced flow of moisture from the Atlantic Ocean and increasingly arid conditions in northern Africa. Until now, it was long believed that the desertification of northern Africa was related to the onset of glaciation on the Northern Hemisphere during the Pliocene and Pleistocene.

Journal reference: Zhang, Z., Ramstein, G., Schuster, M., Li, C., Contoux, C., & Yan, Q. (2014). Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene. Nature, 513(7518), 401-404.

Image: Sand dunes of the Sahara desert at sunset in Fezzan, Libya. Source: Luca Galuzzi, Wikimedia Commons.

Milky Way is part of galactic supercluster Laniakea

Leave a comment

New findings of astronomers at the University of Hawaii presented in Nature show that the Milky Way is part of a gigantic supercluster of galaxies called Laniakea, which means ‘immeasurable heaven’ in Hawaiian. The scientists used a number of telescopes to measure the distances of galaxies to Earth and calculate their peculiar velocities, in order to create a map of the distribution of matter in space. This newly established cosmic map shows the gravitational flows of galaxies, which congregate in clusters and along filaments that are all interconnected in massive superclusters. The existence of these structures has been known for a long time, but their relationships and especially their boundaries were not well defined. Now, the edges of superclusters have been redrawn along the surface where the flows of galaxies start to diverge, similar to water dividing at a watershed. The resulting Laniakea supercluster we call home has a diameter of 500 million lightyears and contains a grand total of 100.000 galaxies with a combined mass of a hundred million billion Suns.

Click here to view the supplementary video, which beautifully illustrates the structure of Laniakea and the flows of its galaxies.

Journal reference: Tully, R. B., Courtois, H., Hoffman, Y., & Pomarède, D. (2014). The Laniakea supercluster of galaxies. Nature, 513(7516), 71-73.

Image: The Milky Way as seen from the Karakoram Range, Pakistan. Source: Anne Dirkse, Wikimedia Commons.

New details on the uplift history of the Tibetan Plateau

Leave a comment

Research of geologists published in GSA Bulletin has revealed new information regarding the uplift history of the Tibetan Plateau, at present the highest elevated mountain range on Earth (~ 4.5 km). The scientists have reconstructed lake paleotemperatures for the Miocene and Pliocene by using clumped isotope thermometry, based on carbonate shells from gastropods in two well-studied basins in central and southwestern Tibet. Their results show that between the late Miocene and early Pliocene, paleotemperatures were up to 9 °C colder than during the mid-Pliocene and younger. Since paleotemperature records reflect changes in both climate and elevation, the scientists estimate that the Tibetan Plateau must have reached an even higher paleoelevation (~ 5.4 km) than at present. This fits well with paleontological and isotopic data from the Miocene-Pliocene indicating the presence of cold-adapted mammals in a cold, high-elevation climate.

Journal reference: Huntington, K. W., Saylor, J., Quade, J., & Hudson, A. M. (2015). High late Miocene–Pliocene elevation of the Zhada Basin, southwestern Tibetan Plateau, from carbonate clumped isotope thermometry. Geological Society of America Bulletin, 127(1-2), 181-199.

Image: North face of Mount Everest as seen from Tibet, China. Source: Luca Galuzzi, Wikimedia Commons.

Corals actively supply nutrients to their environment

Leave a comment

In a new study published in PNAS, corals have been shown to actively manipulate their environment by stirring up currents to supply nutrients to reef ecosystems. The scientists studied six different species of growing reef corals in a laboratory tank and observed their movements with microscopes and video cameras. They found that through small epidermal appendages called cilia, polyps are able to create vortical currents that greatly enhance their exchange of dissolved oxygen and nutrients such as nitrogen and phosphorus with the surrounding water. Coral reefs were previously assumed to be dependent entirely on ambient flow and turbulence for their nourishment, but these results show that they have the ability to actively affect mass transport. This mechanism may be critical to the survival of corals and is likely part of their evolutionary succes.

Click here to watch the accompanying video for a fascinating look at how corals stir up water currents and control nutrient transport.

Journal reference: Shapiro, O. H., Fernandez, V. I., Garren, M., Guasto, J. S., Debaillon-Vesque, F. P., Kramarsky-Winter, E., … & Stocker, R. (2014). Vortical ciliary flows actively enhance mass transport in reef corals. Proceedings of the National Academy of Sciences, 111(37), 13391-13396.

Image: Corals in the Red Sea, Egypt. Source: Mahmoud Habeeb, Wikimedia Commons.

Antarctic sea level rising faster than global sea level

Leave a comment

Climatologists at the University of Southampton have discovered that over the past 19 years, sea level around the coast of Antarctica has risen 2 cm more than the global average rise of 6 cm. They have detected this rapid sea level rise by studying detailed satellite images of an area spanning over a million square kilometers and have attributed it to the melting of fresh water from the Antarctic glaciers and ice shelves, which is further supported by a decrease in the salinity of the surrounding ocean waters. In order to explain these observations, the scientists estimate that a total discharge of approximately 430 Gt of fresh water to the surrounding ocean is required. Furthermore, global ocean circulation model simulations of the effects of melting ice on the Antarctic Ocean closely match their findings.

Journal reference: Rye, C. D., Garabato, A. C. N., Holland, P. R., Meredith, M. P., Nurser, A. G., Hughes, C. W., … & Webb, D. J. (2014). Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge. Nature Geoscience, 7(10), 732-735.

Image: Melting icebergs along the Antarctic Peninsula, Antarctica. Source: Christopher Michel, Wikimedia Commons.

Species extinction rates higher than previously thought

Leave a comment

According to a new study performed by biologists, the current extinction rates of terrestrial animal and plant species associated with human activities may be up to 10 times higher than previously thought. By using fossil datasets and mathematical models, the scientists were able to estimate new natural background rates of species diversification and extinction. Their results indicate that until now, these background rates are likely to have been overestimated and should be in the order of 0.1 extinction per million species per year, rather than 1 extinction per million species per year. Because current rates of extinction are compared against background levels, these new results have major implications for the apparent impact of mankind on life on Earth: the effects may be even more severe than expected.

Journal reference: De Vos, J. M., Joppa, L. N., Gittleman, J. L., Stephens, P. R., & Pimm, S. L. (2014). Estimating the normal background rate of species extinction. Conservation Biology.

Image: Fossil remains of Archaeopteryx displayed in the Museum für Naturkunde in Berlin, Germany. Source: H. Raab, Wikimedia Commons.

1 2