Mass Extinction - DefinitionA significant proportion of species become extinct (between 30% and 95%) The extinctions operate across a wide range ofenvironments and lifestyles The extinctions occurred rapidly (over a few millionyears) and were due to one or more physical factors
5 Major Mass Extinctions identified since the Cambrian Extinction Event Date of ExtinctionEnd of Ordovician 443 Million years agoLate Devonian 375 Million years agoEnd of Permian 251 Million years agoEnd of Triassic 200 Million years agoEnd of Cretaceous 65 Million years ago
The 5 Major Mass Extinctions Gaps between extinctions vary from 51 Ma to 135 Ma with an average gap of 94.5 Ma
Extinctions During the PhanerozoicThe Phanerozoic is from 542 Ma (Cambrian) to the present
Diversity Curves through the Phanerozoic End Triassic Mass Extinction possibly caused by submarine volcanism associated with the break up of Pangea
End of Ordovician Mass Extinction – 443 Ma 70% of marine species became extinctTropical faunas badly affected especially coral reefs Main groups affected Trilobites, Graptolites, Echinoids, Brachiopods
Late Devonian Mass Extinction – 375 MaA series of events that lasted around 10 MaCephalopods, Fish and Corals most affected
End Permian Mass Extinction – 251 MaThe largest mass extinction event removing 95% of marine species and 50% of marine families Trilobites, Cephalopods, Bryozoans, Corals, Crinoids badly affected Major faunal and floral overturn on land Marks the boundary between dominance by the Palaeozoic and Modern Fauna
End Triassic Mass Extinction – 200 Ma Multiple event mostly affected the land where over 95% floral species eliminatedAround 30% marine species became extinct – mainly reef dwellers, Ceratites, Brachiopods and Bivalves
End Cretaceous Mass Extinction – 65 Ma Around 70% of all species wiped outDinosaurs, Reptiles, Ammonites, Belemnites, Brachiopods, Bivalves, Foraminifera
Causes of Mass Extinctions Supercontinent Formation Extra-Terrestrial Impacts Flood Basalt EruptionsMethane Hydrates and Global Warming Rapid and Major Glaciation Events
Supercontinent Formation Pangea formed at the end of the Permian Resulted in fewer continental shelves and lack of habitat for shallow marine organisms Coincided with huge decline in the numbers of shallow marine species Caused rapid fluctuations in climate, unstable weather patterns and extreme aridity in the interior of the land mass
Supercontinent Formation A single continent reduces the input of nutrients to oceans from rivers and estuaries This decreases the amount of nutrients available for shallow water marine life and may have also altered the salinity
Supercontinent Formation A supercontinent positioned close to one of the poles can initiate major glaciations Glaciation causes sea levels to fall and there is a significant reduction in shallow water marine environments A supercontinent located over apole can also lead to the coverage of the Earth in ice, a condition known as ‘Snowball Earth’
Extra-Terrestrial Impacts Asteroids 1 km diameter strike the Earth every 500,000 years Large collisions with 5 km diameterasteroids occur approximately about once every 10 million years The last known impact of an object of 10km diameter or larger was 65Ma
Extra-Terrestrial Impacts Local destruction of habitats – impact blast, shockwave, ignition of wildfiresBillions of tonnes of debris injected into theatmosphere resulting in rapid global cooling
Extra-Terrestrial ImpactsImpact in the sea – billions of tonnes of water vapour injected into theatmosphere resulting in a greenhouse effect and rapid global warming
Flood Basalt Eruptions Eruptions last between 0.5 and 2.0 million years and can erupt enough basalt to coverthe whole of the USA to a depth of a kilometre Local destruction of habitats and initiation of wildfires
Flood Basalt Eruptions Billions of tonnes of carbon dioxide and sulphur dioxide released into the atmosphere during eruptions Both are powerfulgreenhouse gases andwill contribute to veryrapid global warming
Flood Basalt Eruptions When it rains the sulphur dioxide will come back down to Earth dissolved in rainwater andthe acid rain will kill vegetation on a large scale With vegetation dying, all food chains willbe affected and also the oceans may becomeacidified with disastrous effects on marine life
Methane Hydrates in Ocean Floor SedimentsLarge volumes currently locked into ocean floor sediments Stable under low temperatures of deep ocean
Methane Hydrates in Ocean Floor Sediments Global warming may result in deep ocean temperatures rising and the release of large volumes of methane from ocean sediments The rapid release of large amounts of methane into the atmosphere will result in highly accelerated global warming
Glaciations-Possible Causes Supercontinents positionedin high latitudes/close to the poles Milankovitch cycles: Precession, Obliquity and Eccentricity
Glaciations-Effects on Ecosystems Loss of habitat as ice masses grow Could eventually lead to ‘Snowball Earth’ scenario Contraction of climatic belts towards the equatorGlobal cooling, decreased productivity of primary producers
End Cretaceous Mass Extinction – 65 MaA large asteroid or meteorite (10km in diameter) collided with the Earth 65 million years ago
Evidence - Asteroid Impact LocationLocation of possible impact site discovered on the Yucatan Peninsula in Mexico at Chixulub The impact structure is a circular depression about 180 km in diameter
Evidence for Asteroid Impact LocationA BA. Gravity survey onshore and offshore of the Yucatan Peninsula B. 3D map of gravity and magnetic field variations reveals theChicxulub crater, now buried beneath tons of sediment. This view is looking down at the surface, from an angle of about 60°.
Evidence – The K-T Boundary Layer The presence of a thin 2cm layer of iridium-rich clay found all over the world within sedimentary rocks The K-T Boundary Layer dates the same everywhere at 65.5 Ma +/- 0.3 Ma Iridium is a transition element, rare on Earth but found in meteorites. First proposed by Luis Alvarez in 1980
Evidence – Shocked Quartz Shocked quartz is found worldwide, in a thin layer at the boundary between Cretaceous and Tertiary rocks. It was first discovered at nuclear testing sites and later in craters caused by meteorite impacts as at the Barringer Crater near Flagstaff, Arizona in the USA
Evidence – Shocked Quartz Shocked quartz has a microscopic structuredifferent from normal quartz.Under intense pressure, butrelatively low temperature, the crystalline structure of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are calledplanar deformation features (PDFs), or shock lamellae.
Evidence – Tektites (Glass Spherules) Tektites (from Greek tektos, molten) are natural glass rocks up to a few centimetres in size. Most scientists agree they are formed by the impact of large meteorites on Earth’s surface. Tektites (Glass Spherules)from 1 to 8 mm in diameter Tektites are black or olive- are found within a radius green in colour and their of 600 to 1,000km of the shape varies from rounded Chixulub Crater in Mexico to quite irregular.
Evidence – Soot from Wildfires The K-T Layer has high concentrations of carbon in many locations, suggesting that the asteroid impact may have generated wildfires.Large areas of vegetation would have been destroyed in a short time, soot fell to Earth and was incorporated into sedimentary rocks
Evidence – Tsunami Deposits It is thought that the asteroid impact occurred in the sea and initially produced a crater 100 km wide and 30 km deep This would have displaced vast volumes of seawater and generated a series of very large tsunamis possibly over 100 metres in height The tsunamis would have travelled great distances inland, and in Texas at Waco there are large-scale sedimentary deposits thought to be of tsunami origin.
Evidence – Tsunami Deposits The tsunami deposits in Waco, Texas are thought to be from the waves generated by the K-T asteroid impact. The sediments are estimated to have been deposited at least 300km inland by the tsunamis!
Animation to show Impact of a large asteroid with the EarthThe impactors estimated size was about 10 km in diameter and is estimated to have released 4×1023 joules of energy, equivalent to 100,000,000 megatons of TNT on impact.
Origin of the K-T Asteroid Results published in 2007 suggest that the impactor that wiped out the dinosaurs and other life forms on Earth 65 million years ago can been traced back to a break-up eventin the main asteroid belt more than 100 million years earlier.
Flood Basalt Eruptions 66 Ma – The Deccan Traps Erupted mainly over a period of 30,000 years Over 2000 metres thick and cover 500,000 km² May have originally covered 1,500,000 km² Caused a global drop in temperature of 2°C The term Trap is derived from the Dutch for stairs and refers to the step-like landscape of the area