2. What is a Mass 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
• Leading up 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
• Loss of 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
• 65ma Deccan 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 extinctions are 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
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.
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)
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
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)
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.
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
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
