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450 million years ago, the Earth's warm oceans teemed with life we'd recognize as seaweed, starfish, clams, and coral reefs. Suddenly, over half these species died. Now scientists say it was caused by cosmic rays - and could happen again.
Image of a proton shower via University of Chicago.
The biggest effect of cosmic rays on the Earth's atmosphere, says Melott, is on the ozone layer. When radiation events hit the atmosphere-which is 80 percent nitrogen-the bonds between nitrogen atoms break. The nitrogen atoms will then react with anything they can, he explains, and a substantial number of them will react with oxygen molecules or atoms, making oxides of nitrogen, which sets up a chemical reaction that converts ozone back to oxygen. However, stratospheric ozone is a vital shield against ultraviolet light from the sun. So the ozone depletion causes more ultraviolet B light (UVB) than normal to travel through the atmosphere to the ground.
"A strong event like a gamma ray burst from a nearby supernova causes even more depletion, resulting in a doubling of the global average UVB," says Melott, "which all the people who experiment on plants and animals with UVB tell us would be a disaster."
Originally posted by RUSSO
Originally posted by RUSSO
Some more questions:
How many mass extinctions this planet faced through time?
1. Cretaceous–Tertiary extinction event (End Cretaceous or K-T extinction) - 65.5 Ma at the Cretaceous.Maastrichtian-Paleogene.Danian transition interval. The K–T event is now called the Cretaceous–Paleogene (or K–Pg) extinction event by many researchers. About 17% of all families, 50% of all genera and 75% of species went extinct. In the seas it reduced the percentage of sessile animals to about 33%. The boundary event was severe with a significant amount of variability in the rate of extinction between and among different clads. Mammals and birds emerged as domininant land vertebrates in the age of new life.
2. Triassic–Jurassic extinction event (End Triassic) - 205 Ma at the Triassic-Jurassic transition. About 23% of all families and 48% of all genera (20% of marine families and 55% of marine genera) went extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments. The Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia (e.g., Koolasuchus).
3. Permian–Triassic extinction event (End Permian) - 251 Ma at the Permian-Triassic transition. Earth's largest extinction killed 57% of all families and 83% of all genera (53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species) including insects. The evidence of plants is less clear, but new taxa became dominant after the extinction. The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of mammal-like reptiles. The recovery of vertebrates took 30 million years, but the vacant niches created the opportunity for archosaurs to become ascendant. In the seas, the percentage of animals that were sessile dropped from 67% to 50%. The whole late Permian was a difficult time for at least marine life, even before the "Great Dying".
4. Late Devonian extinction - 360-375 Ma near the Devonian-Carboniferous transition. At the end of the Frasnian Age in the later part(s) of the Devonian Period, a prolonged series of extinctions eliminated about 19% of all families, 50% of all genera and 70% of all species. This extinction event lasted perhaps as long as 20 MY, and there is evidence for a series of extinction pulses within this period.
5. Ordovician–Silurian extinction event (End Ordovician or O-S) - 440-450 Ma at the Ordovician-Silurian transition. Two events occurred that killed off 27% of all families and 57% of all genera. Together they are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that went extinct.