The Extinction Event and Life in the Post-Apocalyptic Greenhouse

The Extinction Event and Life in the Post-Apocalyptic Greenhouse
The biggest mass extinction of the past 600 million years (My), the end-Permian event (251 My ago), witnessed the loss of as much as 95% of all species on Earth. Key questions for biologists concern what combination of environmental changes could possibly have had such a devastating effect, the scale and pattern of species loss, and the nature of the recovery. New studies on dating the event, contemporary volcanic activity, and the anatomy of the environmental crisis have changed our perspectives dramatically in the past five years. Evidence on causation is equivocal, with support for either an asteroid impact or mass volcanism, but the latter seems most probable.
The rest of this article spends time speculating through the advances in technology and the reanalyzation of old evidence to determine various cataclysmic events that happened millions of years ago. There are many sections in this article that discuss the methods used to determine the closet possible dates and the sequence in which they follow. There are also sections in this article which discuss methods used for the evidence of impact, eruption and how reading the environmental changes can help paleontologists determine conclusions and narrow the perspectives of paleontologists (scientists) and popular culture as a whole.
However, there are still many factors in the evidence collecting process that make it difficult to determine the actual events, let alone the sequence of them. For instance, at the end of the Permian, giant volcanic eruptions occurred in Siberia, spewing out some 2 million km3 of basalt lava, and covering 1.6 million km2 of eastern Russia to a depth of 400-3000mteres, equivalent to the area of the European Community. Consequently, with increasingly precise dating, the Siberian ?Trap? (areas which are composed of basalt, a dark-colored igneous rock which is generally not erupted explosively from classic conical volcanoes, but usually emerges more slowly from the long fissures in the ground) have switched from having only a minor role in the Permian crisis to being the most probable cause of the whole catastrophe. Some scientists have even suggested recently that the massive flood basalts were actually themselves caused by a giant extraterrestrial impact, which tore deep into the continental crust of that part of present-day Siberia. So this is yet another example the evolutionary and extinction process. The nature of the eruptions casts doubt on such a model, and there is no evidence that any volcanism on the Earth, or indeed on any other planet, was triggered by an impact.
Another angle in which, you can collect and grasp a concept and theorize extinctions is in the readings of the basic environmental changes. The Permian sediments in the ocean were extremely ?bioturbated? (meaning, full of burrows made by a variety of sea creatures feeding and moving through the sediment). These communities both on land and in the ocean were diverse and ecologically complex with many levels in the food chain. For instance, there was evidence of many levels of carnivores like the saber-tooth who fed on thick skinned, rhinoceros-sized herbivores and smaller meat eaters who fed on much smaller pray.

By contrast, sediments deposited immediately after the extinction event, in the earliest Triassic, are dark-colored, often black and full of the kind of rock pyrite. They lack large burrows, and those that do occur are very small, and fossils of marine invertebrates are extremely rare. These observations, in association of the geological evidence, really suggest a dramatic change in oceanic conditions from a well-oxygenated bottom waters to widespread levels of a chemical called benthic anoxia, which suggests a dramatic and even catastrophically occurring of an event. Comparison of the timings of species loss on land an in the sea suggests that they were coincident. In many places, it seems that soils were washed off the land completely, and the only organisms to survive appear to have been fungi.

Geological evidence also points to a rise in the globes temperature to about 6 degrees Celsius due to a raise in the oxygen isotopes. Models of climate have shown how global warming can reduce ocean circulation and the amount of dissolved oxygen which created such high levels of benthic anoxia. A dramatic global rise in temperature is also reflected in the types of sediment and ancient soil deposited on land.

In conclusion life came close to complete annihilation about 251 million years ago. A fortunate 5 percent of species did. It took 100 million years for global diversity at the family level to return to pre-extinction levels. However, ecological recovery was somewhat quicker, with complex communities such as reefs becoming re-established by the Middle Triassic. Little is know currently of the recovery pattern from elsewhere in the oceans, although work is ongoing. On land, for millions of years, virtually the only tetra-pod was the plant-eating Lythtrosurus, surviving on the few surviving herbaceous plants. Forest communities were absent until the Middle Triassic. Life was clearly tough in the ?post-apocalyptic greenhouse?.

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