Located in Hamelin’s Pool, a shallow area of Shark Bay in Western Australia, these odd formations aren’t rocks—they’re stromatolites, and they were built over millennia by single-celled cyanobacteria (also known as blue-green algae). 4,000 to 6,000 years ago, a huge bank of seagrass began to block the tidal flow into Hamelin’s Pool, which meant that the water became twice as salty as the open ocean. Animals like snails and chitons that would usually feed on the algae couldn’t survive, so the blue-green algae began to flourish. Gathered in colonies, they trapped sediment with their sticky surface coatings. This sediment reacted with calcium carbonate in the water and formed limestone, essentially creating a living fossil—this limestone is alive, its top surface layer teeming with active cyanobacteria. The limestone builds up slowly at a rate of about 1mm per year. The stromatolites in Shark Bay are estimated to be between 3,000 and 2,000 years old, but they’re similar to life forms in Precambrian times, 3.5 billion years ago, at the dawn of complex organisms. There are over 50 kinds of cyanobacteria in Shark Bay, and one is thought to have descended from an organism that lived nearly 2 million years ago, making it a part of one of the longest biological lineages.
A hypothesized mechanism for the origin of life, an event called abiogenesis. In this version, called RNA world, small molecules called nucleotides formed in the waters of the early Earth during the Hadean Eon, and polymerized on the surface of clay minerals. These simple chains of RNA could replicate themselves in solution, but only slowly and inaccurately. An RNA molecule developed which would fold into a structure that catalyzed RNA polymerization; a ribozyme. The first ribozymes would replicate their sister strands, and produce copies of themselves and other RNA molecules.
In the same environment, long chains of carbon molecules called phospholipids were formed. These molecules have two parts, the tail, which is hydrophobic, and the head, which is hydrophillic. Because of these properties phospholipids will stick together and form micelles and vesicles in water. Vesicles can absorb RNA nucleotides, concentrating them and creating a space where they can replicate, mutate and evolve. At some point a ribozyme became enclosed within a vesicle, starting a chain reaction that evolved into the multitude of biological forms that we see today.
Because this event occurred more than 3.8 billion years ago, theories about how and where it happened are highly speculative. Possible environments for abiogensis include hydrothermal vents on the ocean floor, hyper saline bubbles of water trapped in ice, radioactive lakes or lagoons on earths surface, and even in space or on another planet, brought to earth through a panspermia event. We have very little molecular evidence of the first cells, but ribozymes and catalytic RNA molecules are embedded in the DNA replication machinery of all life. Because evidence of this event has almost certainly been lost to time, the true mechanisms of the origin of life may remain a mystery to science.
dionys moser photographs the alien like landscape of the ethiopian dallol hydrothermal field, a vast area of uplifted thick salt deposits affected by intense fumarolic activity, famous for being the only known volcanic area bellow sea level and for being both the hottest place on the planet, with average annual temperatures well above 30 degrees celsius, and the most colourful, with its pools of a hot sulfuric acid brine and ferrous multicolored salt deposits.
A dirty thunderstorm (also, Volcanic lightning) is a weather phenomenon that occurs when lightning is produced in a volcanic plume. A study in the journal Science indicated that electrical charges are generated when rock fragments, ash, and ice particles in a volcanic plume collide and produce static charges, just as ice particles collide in regular thunderstorms.
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. Because stars, which comprise most of the visible matter in the universe, are composed mostly of hydrogen and helium, astronomers use for convenience the blanket term “metal” to describe all other elements collectively. Thus, a nebula rich in carbon, nitrogen, oxygen, and neon would be “metal-rich” in astrophysical terms even though those elements are non-metals in chemistry. This term should not be confused with the usual definition of “metal”; metallic bonds are impossible within stars, and the very strongest chemical bonds are only possible in the outer layers of cool K and M stars. Earth-like chemistry therefore has little or no relevance in stellar interiors.
The metallicity of an astronomical object may provide an indication of its age. When the universe first formed, according to the Big Bang theory, it consisted almost entirely of hydrogen which, through primordial nucleosynthesis, created a sizeable proportion of helium and only trace amounts of lithium and beryllium and no heavier elements. Therefore, older stars have lower metallicities than younger stars such as our Sun.
Image credit:NASA, ESA, and H. Richer (University of British Columbia)
arcadians: Dione. photographed by Cassini, 28th March 2012.
Evander Crater and central peak complex, 57°S 145°W. At 350km wide, Evander is the biggest crater on Dione. At bottom left is half of Erulus Crater and its central peak.
In legend and poem, Evander was a wise king of Arcadia, and an ally of Aeneas in the Trojan war. As far as I know the crater’s central peak has no name; “Mt. Pallantium” might serve, after the city that Evander founded, later to become part of Ancient Rome.
Erulus is a curious and obscure character, possibly mythological but only recorded in Vergil’s Aeneid; he was born of the fertility-harvest goddess Feronia, and had three souls and six arms. Accordingly, Evander was compelled to kill him three times before he was slain.