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Mass Extinctions in Earth's History

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Allison Prost

on 18 April 2013

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Transcript of Mass Extinctions in Earth's History

Marine Life The extinction rate of marine organisms was catastrophic with over 96% of marine species extinct. There was a major drop of CO2 levels in the ocean, also a loss of oxygen, there was carbon dioxide poisoning and rapid global warming. It primarily affected organisms with calcium carbonate skeletons, especially those reliant on ambient CO2 levels to produce their skeletons. During the Triassic age, diversity rose rapidly but remained low. Terrestrial vertebrates Over two-thirds of terrestrial amphibians/mammal-like reptiles families became extinct. Even the groups that survived suffered extremely heavy loss of species, and some terrestrial vertebrate groups nearly became extinct at the end-Permian age. Land vertebrates took an unusually long time to recover from the P–Tr extinction, about 30 million years after the extinction in the late Triassic period. At that time the dinosaurs, pterosaurs, crocodiles, archosaurs, amphibians, and mammals were abundant and diverse. Mass Extinctions in Earth's History By Joshua Pavlica, Alex Kocsik, Allison Prost, and Marcus Peterson Permian-Triassic Causes Impact Event Volcanism Sea level fluctuations Anoxic Event Pangaea Some reported evidence for a major impact event is the finding of extremely rare shocked quartz in Australia and Antarctica. However, the accuracy of these claims have been challenged; the quartz in Antarctica has been found to actually be produced by plastic deformation. Although you would think the crater from such an impact would still exist, it is most likely that the asteroid would have fallen into the ocean. If this had happened, there would not even be a crater at the ocean's floor because it is constantly changing; the crust is never more than 200 million years old. Ordovician-Silurian The Ordovician–Silurian extinction event, more commonly the Ordovician extinction, was the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and overall loss of life. Basic Facts The Ordovician extinction occurred between about 450 Ma to 440 Ma ago.
Consisted of two bursts of extinction that were separated by one million years.
More than 60% of marine invertebrates died, including two-thirds of all brachiopod and bryozoan families.
All known life at the time was confined to the seas and oceans.
The foremost cause of extinction appears to have been the movement of Gondwana into the south polar region. Gondwana Gondwana is the name given to the more southerly of two supercontinents (the other being Laurasia) which were part of the Pangaea supercontinent that existed approximately 510 to 180 million years ago.
Gondwana is believed to have sutured (the joining together of a fault zone) between 570 and 510 million years ago.
It separated from Laurasia 200-180 Million years ago during the mid-Mesozoic era while Pangea was breaking up. Gondwana drifted towards the South Pole after the split from Laurasia.
Gondwana included most of the landmasses in today's Southern Hemisphere, including Antarctica, South America, Africa, Madagascar and Australia, as well as the Arabian Peninsula and the Indian subcontinent. More About Gondwana The continent of Gondwana was named by Austrian scientist Eduard Suess after the Gondwana region of central northern India from which the Gondwana sedimentary sequences are described.
Gondwana's movement southward led to global cooling, glaciation, and consequent sea level fall.
The falling sea level disrupted or eliminated habitats along the continental shelves.
Evidence for the glaciation was found through deposits in the Sahara Desert.
A combination of lowering of sea level and glacially-driven cooling are likely driving agents for the Ordovician mass extinction. An Excerpt From “The Late Ordovician Mass Extinction” in the Annual Review of Earth and Planetary Sciences “The cause [of the Ordovician mass extinction] was a brief glacial interval that produced two pulses of extinction. The first pulse was at the beginning of the glaciation, when sea-level decline drained epicontinental seaways, produced a harsh climate in low and mid-latitudes, and initiated active, deep-oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths. Following that initial pulse of extinction, surviving faunas adapted to the new ecologic setting. The glaciation ended suddenly, and as sea level rose, the climate moderated, and oceanic circulation stagnated, another pulse of extinction occurred. The second extinction marked the end of a long interval of ecologic stasis.” More About the Pulses of Extinction The pulses of the mass extinction appear to correspond to the beginning and end of the most severe ice age of the Phanerozoic era, which marked the end of a longer cooling trend in the Hirnantian faunal stage towards the end of the Ordovician, which had more typically experienced greenhouse conditions.
The event was preceded by a fall in atmospheric CO2, which selectively affected the shallow seas where most organisms lived (as they had less food to eat).
As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it. Glaciation locks up water from the world-ocean, and the interglacials (a time between ice ages) free it, causing sea levels to repeatedly drop and rise.
The vast intra-continental Ordovician seas withdrew and eliminated many ecological niches. They then returned, starting a minor revival of species. However, the seas withdrew again with the next pulse of glaciation, eliminating biological diversity at each change and halting any revival of the species.
The end of the second extinction event occurred when melting glaciers caused the sea level to rise and stabilize once more. The rebound of life's diversity with the sustained re-flooding of continental shelves at the onset of the Silurian period saw increased biodiversity within the surviving species. One common hypothesis concerning an impact event is that it would have triggered several other catastrophic events such as... Debate! Natural Causes of Extinction Meteor Strikes Supervolcanoes Global Warming/
Methane Bursts Solar Flares NASA’s JPL (Jet Propulsion Laboratory) Near Earth Asteroid Tracking team says that:
"The most dangerous asteroids, capable of a global disaster, are extremely rare. The threshold size is believed to be 1/2 to 1 km. These bodies impact the Earth only once every 1,000 centuries on average. Comets in this size range are thought to impact...once every 5,000 centuries or so."
The Asteroid and Impact Hazard page says that:
"The threshold for an impact that causes widespread global mortality and threatens civilization almost certainly lies between about 0.5 and 5 km diameter, perhaps near 2 km. Impacts of objects this large occur from one to several times per million years.” NASA’s JPL (Jet Propulsion Laboratory) Near Earth Asteroid Tracking team says that:
"The most dangerous asteroids, capable of a global disaster, are extremely rare. The threshold size is believed to be 1/2 to 1 km. These bodies impact the Earth only once every 1,000 centuries on average. Comets in this size range are thought to impact...once every 5,000 centuries or so."
The Asteroid and Impact Hazard page says that:
"The threshold for an impact that causes widespread global mortality and threatens civilization almost certainly lies between about 0.5 and 5 km diameter, perhaps near 2 km. Impacts of objects this large occur from one to several times per million years.” Near Earth Objects As of last month, 9,683 NEOs have been discovered, including 93 near-Earth comets and 9,590 near-Earth Asteroids.
Of those there are 751 Aten asteroids, 3,613 Amor asteroids, and 5,214 Apollo asteroids.
There are 1,360 NEOs that are classified as potentially hazardous asteroids (PHAs) that have an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 AU or less.
Currently, 155 PHAs and 861 NEAs have an absolute magnitude of 17.75 or brighter, which roughly corresponds to at least 1 km in size. Impact From an article by HowStuffWorks "Let's say that an asteroid the size of a house crashed on Earth at 30,000 mph. It would have an amount of energy roughly equal to the bomb that fell on Hiroshima -- perhaps 20 kilotons. An asteroid like this would flatten reinforced concrete buildings up to half a mile from ground zero, and flatten wooden structures perhaps a mile and a half from ground zero. It would, in other words, do extensive damage to any city.

If the asteroid is as big as a 20-story building (200 feet on a side), it has an amount of energy equal to the largest nuclear bombs made today -- on the order of 25 to 50 megatons. An asteroid like this would flatten reinforced concrete buildings five miles from ground zero. It would completely destroy most major cities in the United States.

By the time you get up to a mile-wide asteroid, you are working in the 1 million megaton range. This asteroid has the energy that's 10 million times greater than the bomb that fell on Hiroshima. It's able to flatten everything for 100 to 200 miles out from ground zero. In other words, if a mile-wide asteroid were to directly hit New York City, the force of the impact probably would completely flatten every single thing from Washington D.C. to Boston, and would cause extensive damage perhaps 1,000 miles out -- that's as far away as Chicago. The amount of dust and debris thrown up into the atmosphere would block out the sun and cause most living things on the planet to perish. If an asteroid that big were to land in the ocean, it would cause massive tidal waves hundreds of feet high that would completely scrub the coastlines in the vicinity." Late Devonian Extinction There is sound evidence that the Emeishan and Siberian Traps--located in China and Russia--contributed to flood basalt eruptions at the end of the Permian era. These eruptions may have caused dust clouds and acid aerosols that blocked out sunlight and disrupted photosynthesis both on land and in the photic zone of the ocean, causing food chains to collapse. These eruptions could have caused acid rain when the aerosols washed out of the atmosphere. The acid rain could kill land plants and water plant, such as mollusks and planktonic organisms, which had calcium carbonate shells. The eruptions would have also emitted carbon dioxide, causing global warming.

However, some scientists speculate that these volcanic eruptions were not powerful enough to single-handedly cause a mass extinction. But they do agree that volcanism could have contributed to even more factors, including... Basics:
-Occured 374 million years ago
-Differs from the other 4 extinctions in that it occurred within the last epoch of the Devonian Period, and not at the end of a geological period
-82% of species wiped out
-Occurred in 5 main pulses over the course of 1-1.5 myr
1.Lower Kellwasser event
Followed by 3 upperkellwasser events (500-800 kyr later)
2.At base of upper kellwasser limestone unit
3.Within the unit
4.At the top of the unit (more severe than the prior two)
5.Homoctenid event (in the earliest Famennian period)- called this because the homoctenids were the only cricoconarids to survive up until this point and then were killed Possible Causes (Organized in models that account for many causes) Global Anoxia Many causes have been assumed for the event: asteroid impact, flood basalt eruptions, volcanism, catastrophic methane release, a drop in oxygen levels, sea level fluctuations or some combination of these. So what is anoxia? Anoxic water is water that is depleted of oxygen, and thus many organisms cannot survive. Let's look at some evidence. Permian-Triassic mass extinction happened about 252.28 Ma (million years) ago, it's been nicknamed The Great Dying. The Earth's most severe known extinction event, with up to 96% of all marine and 70% of terrestrial vertebrate species becoming extinct. Since so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, possibly up to 10 million years. A solar flare is a sudden brightening observed over the Sun's surface, which is interpreted as a large energy release of up to 6 × 10^25 joules of energy or 160,000,000,000 megatons of TNT equivalent. Blasts of energetic solar cosmic ray particles that are shot out with the eruption of a solar flare, can arrive with little advanced notice, traveling the 93 million mile distance from the Sun to the Earth in a matter of hours. The flare ejects clouds of electrons, ions, and atoms through the corona of the sun into space. These clouds typically reach Earth a day or two after the event. Other devices operating at these frequencies, X-rays and UV radiation, emitted by solar flares can affect Earth's ionosphere and disrupt long-range radio communications. Direct radio emission at decimetric wavelengths may disturb operation of radars as well. Deep water species were surviving because of their already high tolerance for low oxygen conditions, while....... ......shallow water organisms were not able to survive. They did not have tolerance for low-oxygen conditions, especially in fresh-water conditions. Black shale is formed by the compaction of unoxidized carbon. Black shale was found globally in water from this period. -50% of genera went extinct

-Most extinctions occured for marine life, not land organisms

-Reefs and fresh water regions were almost entirely depleted Before Extinction: -Land was separated by Godwana, Euramerica, and siberia

-Oceans were full of reefs built by the stromatoporoids

-Lands were inhabited by plants and insects mainly After Extinction: Oceanic Overturn Poisonous water from
the deep ocean Fresh, shallow water To account for changes of temperature and its effect during this extinction, many overturns would have had to occur. Problem with this Model Global Cooling A global cooling would account for all the same effects seen from a global turnover.

In addition, a global cooling explains why water-surface plankton and some terrestrial species that live close to the water went extinct, not just those that lived within the water.

The extinction happened in the 5 pulses, and the time frame of those is very similar to glacial cycles in other periods. Multiple Impacts -Around 6-10 known impact craters have been found that date back to the late Devonian

-Very few, however correspond with the extinction pulses of the era

-Imapcts would have accounted for a global cooling

-Impacts in Australia in the early crepida Zone could possibly have been influential during the Late Devonian extinction, except it is hard to tell due to the concentrations sediments (still trying to date them) So, what caused the extinction? Many of the theories involve multiple causes, becuase it's hard to say if one thing caused the whole extinction Because there were 5 pulses to the extinction, it's hard to say if they were all actually related or if each event had its own cause. During the first 2 events marine organisms were killed, while during the last 3 it was mainly surface-water plankton that suffered. Evidence during this period for anoxia, or severe oxygen deficiency, is apparent in the Tethys and Panthalassic Oceans. This spread of toxic, oxygen-depleted water would have been devastating for marine life, producing widespread die-offs. This evidence may also explain the slow recovery of marine life after the extinction. Anoxia could have started from the warming from the enhanced greenhouse effect after the eruptions of the Siberian Traps. This warming would have reduced the solubility of oxygen in seawater, causing the concentration of oxygen to decline. Although Pangaea would not have been directly responsible for the "Great Dying" and the end of the Permian, it would have decreased the extent of shallow aquatic environments. Many organisms depend on this complex ecosystem, and would have died out. Furthermore, the joining of essentially all of the landmass would have altered both oceanic circulation and atmospheric weather patterns, creating seasonal monsoons near the coasts and an arid climate in the vast continental interior, creating a new ecosystem for the life on land. As we saw in the Permian-Triassic extinction, supervolcanoes can
contribute to many long-term problems beyond earthquakes and lava flow. They can cause major harm to the atmosphere by emitting dust clouds and acid aerosols into the sky. Additionally, acid rain from the explosion would quickly kill land and aquatic plants. Another major consequence of a massive volcanic eruption would be the emission of carbon dioxide, causing global warming. The latest super-massive volcanic eruption was only 197 years ago--in the year 1815--in Indonesia. The year following was nicknamed the "Year Without a Summer" because of the massive global temperature drop. This eruption ejected immense amounts of volcanic ash into the upper atmosphere, causing a dry fog that blocked the sunlight. The drop in temperature did not simply increase sales in winter coats and furs; it demolished crops causing a famine, and created deadly floodings. It is estimated that, at the rate that we produce carbon and burn fossil fuels, the planet's average temperature could raise as much as 42.6 degrees by the end of the century. With this rise in temperature would come arid deserts (similar to in the Great Dust Bowl) and the loss of fresh water sources. People will die of heat strokes, loss of resources, and unlivable conditions that cannot support our population. Methane bubbbles have been known to sit in the depths of the ocean, and once they erupt , they cause catestrophic extinction in many species. In the Permian extinction, a methane bubble exploded that wiped out 96% of species. During the Late Paleocence Thermal Maximum, another bubble burst that wiped out similar numbers. Although that eruption was not enough to wipe out the human race, it wasn't even close to the most massive eruption in Earth's history. That position belongs to the eruption of Lake Toba--also in Indonesia--about 74,000 years ago. According to the Toba Catastrophe Theory, if this eruption were to occur today, it would wipe out at least 60% of the human population. Although this isn't quite at 100%, volcanic eruptions are happening constantly and the next supervolcanic eruption is bound to happen soon. Especially now after many oil spoils such as the massive BP spill, the penetration into oil reserves in the ocean floors might have set the conditions for a massive methane bubble to be released that would cause mass extinctions. In the Gulf, there are already signs of methane gas leaking from fissures in the ocean floor, a prescursor to the release of a methane bubble.
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