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Jaimie pres
Mass extinctions occur over a geologically short period of time and involve the widespread death of many species across different ecosystems. The K-T extinction that killed the dinosaurs 65 million years ago is a prominent example. Initially, evidence pointed to a catastrophic cause, and Walter Alvarez first proposed the impact theory - that an asteroid collision caused the extinction. This theory is supported by evidence of an iridium anomaly and shocked quartz found in rock layers from the time. Alternatively, massive volcanic eruptions in the Deccan Traps could have released greenhouse gases and sulfur, warming the planet over centuries in a similar way to an impact. While rare events like impacts and huge eruptions may have caused some extinctions, more
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Jaimie pres
- 1. Mass Extinctions Causes andEffects By Jaimie Clifford
- 2. What is aMass extinction • Large range of families affected • Variety of different ecosystems • Happens over a geologically short period of time • Mass extinction caused by an independent event from background extinctions
- 3. K-T Extinction • Leadingup to the K-T boundary Dinosaur fossils and some other extinct families are present. • These disappear completely above the K-T boundary. • This was known for a long time, but Walter Alvarez first studied it in detail. • Alvarez put forward the case for a catastrophic mass extinction at this time.
- 4. K-T Theories • Lossof Sex Drive • Rise of the Mammals • Supernova • Impact theory • Volcanic Eruptions
- 5. Impact theory • Evidence– Iridium anomaly, Shocked Quartz, Tektites, Fern Spike and a Crater at Chicxulub. • Short-term effects – Total local destruction, forest fires, Impact winter, food chains collapse. • Long-term effects – Cooling and acid rain, Centuries of a greenhouse planet.
- 6. Volcanic Eruptions • 65maDeccan traps were erupting, releasing greenhouse gases and Sulphur into the stratosphere • Short-Term effects – Ash may have blocked out the sun locally, mainly a long-term issue • Long-Term effects – Similar to a Impact scenario, greenhouse planet and possible ocean anoxia
- 7. Issues and flaws •Not all organisms were equally affected • Other impact an eruption examples caused no effect • Damage closer to crater seems much more severe than further away • Rare impacts and huge eruptions are so rare that other more common causes must be looked at before falling back on the rarer causes
- 8. Conclusion • Mass extinctionsare part of the natural evolution of life • Although its study may seem entirely academic… • It is important, as currently we are in a mass extinction, caused by humans
- 9. Thank you forlistening, any questions?
Editor's Notes
- #3 The number of extinct taxa is much higher than regular extinctions.The event happens very suddenly and quickly in geological time.The event affects several taxa across the phylogenetic and geological age spectrum.The event affects several ecosystems and biomes, not necessarily in the same way.The event has a geographically wide reach, often global, but not necessarily so.The cause of the mass extinction differs from the cause of the background extinction, qualitatively and/or quantitatively.The cause of mass extinctions is independent of the cause of background extinctions, although the cause of the background extinctions may exacerbate the mass extinction.The recovery from mass extinctions proceeds by the spreading of previously non-dominant taxa (e.g. mammals after dinosaurs) or of new taxa (e.g. Archosaurs after the P-T), or by restructuring of ecosystems (e.g. post-Ordovician).Sepkoski curve. Ordovician – Silurian, Late Devonian, Permo-Triassic (4% survived) Tr-J, K-T.
- #4 Half of all animal genera died out, the large reptilian creatures died out (marine and terrestial) forams went back to uncomplicated states, annomites died out. Life dramatically changedFirstly dinosaurs lived a very long time (stegosaurus to T-rex) Forams changed micro fossilsPollen count (angiosperms to ferns) (fern spike)No one cared before as they assumed it was a time gap in the record/ a gradual declineAlvarez realised that the with radiometric dating the time of extinction was a few ma (magnetic stripes indicate event in 0.5ma)
- #5 Old theories like paloweltschmertz have died out as other organisms were seen to have died out too.However dinosaurs may have already been in decline as mammals too over, but unlikely to have wiped them all out.Supernova explains iridium, but lack of plutonium – 244 Main two theories are in fact impact and Volcanic eruptions
- #6 10Km wide bolide (larger than everest)9 ppB were found of iridium compared to the expected 0.5Shocked quartz has multiple layers of deformity due to huge pressures not creatable in a terrrestial environmentTekkites (spherules of glassy rock)Fern spike after iridium annomaly points to devestation (kileuea) and crater (geophysical surveys)Shockwave + tsunami destroys local area. Returning ejecta spontaneously ignites forests, very similar to nuclear winter, blocks out sun for possibly years (definitely months), plants die, food chain collapsesThe Impact rock (anhydrite) contained 100billion tons of sulphur, 10trillion tons of CO2 – acid rain (nitric acid too) (ocean anoxia/acidification battery acid in strength (oxygen recycling stopped and hard parts dissolved surface of ocean is barren for 20years, sulphur loving bacteria rise to surface, ocean life dies out) (many variables for life changed)Extreme scenarios involve hypercanes due to ejecta (not this severe)
- #7 2million km2 area, lasted 1ma either side of boundary maximumEruption rate therefore huge even if continuousFire fountains would blast ash and CO2 into the stratosphere to spread (Tambora caused widespread hunger)Cooling then warming with acid rain as wellP-Tr was caused possibly by Siberian traps and only 4% of life survived that. Seems too coincidental.
- #8 Some of the patterns are expected, smaller animals which can burrow and scavenge survive (mammals and small lizards) also river communities living of detritus survive better than mostSo do high- latitude animals which adapt better, and deep-sea organisms are more resistant to shallow marine organismsHowever some do not match: ESD, large birds, plants far away from impact site (japan)May be a threshold potential, or both combined may have caused the extinction
- #9 Gradualismvs catastrophismWithout mass extinctions humans would not be hereAnalysing the effects of mass extinctions and the time it takes for recovery to occur may help us modify our actions and stop us plumeting over an edge which we cannot return from