Extinction

It is commonly said that the final fate of all the species is Extinction, that is, //animal and plant species appear and eventually disappear they do not longer exist on Earth.// The cause of the extinction; however, is variable. For example, in the process known as pseudoextinction the species evolves into a new species that differs so much from its ancestral group that the parent species can be considered as extinct although in the strict sense no extinction event occurred. In other cases//the species dies out (disappears) without giving origin to anything else//, this process is know as an extinction. Furthermore, //there are times or episodes in the geological past in which the extinction rates are greatly accelerated resulting in the marked decrease in the diversity of organisms.// Such extinction that involves the disappearance a number of groups is known as mass extinction.

[|Back to top] During geologic history, there have been times when large groups of organisms became extinct within a short period (a few million years)- some of these mass extinction have been used to define period breaks. Main episodes of mass extinction in the history of the biosphere include: **1) Cambrian/Ordovician**, 505 my ago: Many trilobites, sponges, and gastropods. About 52 percent of biota involved. ** 2) Ordovician-Silurian extinction **, about 439 million years ago, caused by a drop in sea levels as glaciers formed, then by rising sea levels as glaciers melted. The toll: 25 percent of marine families and 60 percent of marine genera. **3) Devonian/Mississippian,** 360 my ago: groups of corals, trilobites, bryozoan and fish. About 30 percent of the biota involved. **4) Late Devonian extinction**, about 364 million years ago, cause unknown. It killed 22 percent of marine families and 57 percent of marine genera. Erwin said little is known about land organisms at the time. **5) Permian/Triassic,** 251 my ago: Rugose corals, trilobites, blastoids, brachiopods, and foraminifera became extinct. About 50 percent of the biota involved. Many scientists suspect a comet or asteroid impact, although direct evidence has not been found. Others believe the cause was flood volcanism from the Siberian Traps and related loss of oxygen in the seas. Still others believe the impact triggered the volcanism and also may have done so during the Cretaceous-Tertiary extinction. The Permian-Triassic catastrophe was Earth�s worst mass extinction, killing 95 percent of all species, 53 percent of marine families, 84 percent of marine genera and an estimated 70 percent of land species such as plants, insects and vertebrate animals. **6) The End Triassic extinction**, roughly 199 million to 214 million years ago, most likely caused by massive floods of lava erupting from the central Atlantic magmatic province -- an event that triggered the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain. The death toll: 22 percent of marine families, 52 percent of marine genera. Vertebrate deaths are unclear. ** 7) Jurassic/Cretaceous **, 144 my ago: Ammonites, brachiopods, and fish groups. About 35 percent of biota involved.  **8) Cretaceous/Tertiary,** 65 my ago: Ammonites, dinosaurs, marines reptiles become extinct, many types of marine invertebrate were affected. 26 percent of biota involved. **Cretaceous-Tertiary extinction**, about 65 million years ago, probably caused or accelerated by impact of a several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico. Some argue for other causes, including gradual climate change or flood-like volcanic eruptions of basalt lava from India�s Deccan Traps. The extinction killed 16 percent of marine families, 47 percent of marine genera (the classification above species) and 18 percent of land vertebrate families, including the dinosaurs.

** The Causes of Mass Extinctions ** **Plate Tectonics:** the joining of all the continents into one supercontinent, Pangaea, destroyed much of the suitable shallow-water, marine, continental shelf area. During times of active plate tectonics continents join, and faunal diversity appears to decrease. When continents fragment, faunal diversity increases. Plate tectonics is invoked as the main cause of Paleozoic extinctions. **Climatic Changes:** Glaciations, global warming events **Extraterrestrial Impacts:** A controversial hypothesis for mass extinctions has been postulated, particularly for the extinction of the dinosaurs at the end of the Cretaceous--extraterrestrial meteor or asteroid impacts. While meteors and/or asteroids have certainly struck the earth In the past, the causal relationship between impacts and extinctions is still debated. **Humans and human activities** should be listed as a cause of extinction of species. As we know there is a long list of endangered biota (animals and plants) due to human intervention on the environment or by direct abuse of species.

** FOSSILS AND THE [|GEOLOGIC TIME SCALE] ** The fossil record shows many evolutionary (new appearance) and extinction (disappearance) events, From an examination of the timing of these events, geologists have been able to divide geologic time into major units based on the history of life. Phanerozoic time (from about 700 million years ago to the present) is divided into three eras-Paleozoic, Mesozoic, and Cenozoic the basis of the overall nature or predominant character of fossils found in the strata. The -subdivision of eras into periods is clone primarily on the basis of extinction events, In general, the Paleozoic fossil record is water marine invertebrates characterized by shallow-water marine invertebrates. Thus, the Paleozoic is sometimes called the Age of Invertebrates. The Mesozoic rock record contains a relatively large percentage of continental deposits with fossils of reptiles. hence, the Mesozoic has been termed the Age of Reptiles. The Cenozoic fossil record contains a large number of mammals and flowering plants that evolved during this time. The Cenozoic is informally named the Age of Mammals. http://www.bbc.co.uk/nature/extinction_events http://www.nature.com/nature/journal/v471/n7336/fig_tab/nature09678_T1.html

Nova: Permian Extinction https://www.youtube.com/watch?v=y6ig6zKiNTc https://www.youtube.com/watch?v=eG8XyesAu74

http://www.pbs.org/wgbh/nova/nature/dinosaur-plague.html

Should extinct animals be revived? Seminar. https://www.ted.com/talks/hendrik_poinar_bring_back_the_woolly_mammoth?language=en Great Pyramids started before mammoth went extinct.

The loneliest frog on Earth  is dead, taking with him the hope of an entire species. http://www.huffingtonpost.com/entry/toughie-loneliest-frog-dead_us_57f33c4ee4b01b16aafebb0c?section=us_science

[|The most numerous bird species in the history of our planet.] https://www.fieldmuseum.org/science/blog/year-passenger-pigeon Bring back from extinction https://newsela.com/articles/passenger-pigeons/id/5050/

[|Documentary Racing Extinction] http://www.wired.com/2015/11/racing-extinction-louis-psihoyos/

https://qrius.si.edu/jump/extinction-over-time#.VTGJ-NzF_sE https://qrius.si.edu/watch/preparing-extinct-toothed-whale#.VTGJodzF_sE = The Day the Mesozoic Died = https://www.youtube.com/watch?v=tRPu5u_Pizk https://www.youtube.com/watch?v=F1s6aVUxjKk

http://www.hhmi.org/biointeractive/article-day-mesozoic-died http://www.scientificamerican.com/article/fact-or-fiction-dark-matter-killed-the-dinosaurs/

http://www.popsci.com/woolly-mammoth-dna-brought-life-elephant-cells http://news.yahoo.com/woolly-mammoth-thylacine-guide-helps-choose-species-resurrect-132534998.html

http://www.latimes.com/science/sciencenow/la-sci-sn-ocean-acidification-mass-extinction-20150409-story.html http://www.latimes.com/science/sciencenow/la-sci-sn-ocean-acidification-west-coast-20130725-story.html

Should animals be brought back from extinction? http://www.cnn.com/2014/05/02/opinion/sutter-jurassic-park-endangered/index.html

Tasmanian tiger Wildlife scientists have re-opened the cryptic case of a carnivore that resembled a striped coyote and vanished from its Australian haunt nearly 80 years ago. While the scientists think chances are slim that the so-called Tasmanian tiger (//Thylacinus cynocephalus//) still roams the island off the coast of Australia, they can’t help but turn over every possible leaf to look for evidence of the elusive animal. The last wild Tasmanian tiger was killed between 1910 and 1920, and the last captive one died in 1936 at the Hobart Zoo in Tasmania, Australia. In 1986, the creature was declared extinct. The extinction marked the demise of the only member of its family, //Thylacinidae//, and the world’s largest marsupial (pouched) carnivore. It weighed about 65 pounds and had a nose-to-tail length of six feet.

However, rumored sightings of the creature continue to emerge from the island's ancient forests. Now zoologist Jeremy Austin of the Australian Center for Ancient DNA and his colleagues are examining [|DNA] from animal droppings found in Tasmania in the late 1950s and 1960s, which have been preserved in the Tasmanian Museum and Art Gallery. Eric Guiler, a //thylacine// expert who found the scats, said he thought the droppings probably came from the Tasmanian tiger rather than a dog, Tasmanian devil or a quoll, according to Austin. “If we find //thylacine// DNA from the 1950s scats it will be significant,” Austin said. “This would prove that either the //thylacine// produced the scat or a [Tasmanian] devil ate a thylacine and dropped the scat. Either way that is proof that the thylacine was there at the time.” If they were to find evidence the Tasmanian tiger was alive between its last sightings in the wild (between 1910 and 1920), that would mean the beast was hidden from humans for 40 to 50 years. “If they could survive this long with no real physical proof, then it does add a little more hope to the possibility that they could survive another 50 years without ever being caught, killed [or] hit by a car,” Austin told //LiveScience//. “This chance is of course not great, but the glimmer of hope is ever so slightly brighter.”