2. • Occurs when the last representative of a
taxon dies.
• For Earth History, extinction is the last, or
most recent, occurrence of an identifiable
fossil.
3. MASS EXTINCTION
• Greater than 50% of all species die at similar
time
• Geologically short intervals of intense
species extinction
6. Patterns during Mass Extinction
Occurs in both terrestrial and marine
environments
On land, animals suffer yet plants seem highly
resistant
Disappearance of tropical life forms
Tendency of certain animal groups to experience
and survive (trilobites and ammonoids)
Periodicity in geological time (occurring about
every 26 million years)
7. Extinction Agents
• Catastrophic
• Extraterrestrial impacts such as meteorites
or comet showers
• Geologic
• Volcanism, glaciation, sea levelvariations,
global climactic changes, oxygen/salinity
level changes in ocean
9. Victims
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Many species of coccolithophorid: never recover diversity
Many species of foram
All ammonoids
All belemnoids
All rudists
All plesiosaurs
All mosasaurs
All pterosaurs
All non-flying dinosaurs
Several clades of birds
Many mammal groups (only monotreme prototheres, multituberculate allotheres, the ancestors
and closest relatives of the marsupials among the metatheres, and the ancestors and closest
relatives of the placentals among the eutheres)
10. Proposed Causes: The Maastrichtian
Regression
Draining of epeiric seas would alter terrestrial
climate
11. Increased Maastrichtian volcanism,
especially the Deccan Traps
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Decrease insolation (incoming sunlight) by presence
of fine particles in high atmosphere
Also change Earth's albedo, although not as
dramatically
Would operate on the scale of a few tens of
thousands to hundreds of thousands of years
12. The Chicxulub Impact
• 1980 – Walter Alvarez
• Hypothesized: an asteroid impacted Earth at
the K/T boundary
• Evidence:
• Iridium
• Shocked Quartz
• Tektites
19. Probable Effects
Short term:
• Release lots of energy near impact, form
huge crater: 1.8 x 108 megatons!!
• Burst of light would vaporize material for
kilometers around, just like thermonuclear
weapons
• Blast wave would devastate nearby region; it
would be felt around the world, but decrease
with distance
• Shockwaves from impact would generate
huge tsunamis ("tidal" waves)
20. Longer term:
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Material vaporized by impact kicked high up in
atmosphere: reduced amount of incoming sunlight
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Observations on Mars showed big temperature
drops due to high-level particles
In human history, eruption of Tambora in
Indonesia in 1815 produced chilling effects
worldwide for more than a year later
Dust and ash would block out sunlight, reducing
photosynthesis and killing off plants on land and
surface algae in water; herbivores feeding on these
would die; carnivores feeding on these would starve
(after a brief feast)
Collapse of foodwebs would require long term to
The problem with these definitions is that they are too broad. Other factors must be considered.
Mass extinctions are harder to pin down than it might seem, and the task becomes more difficult the farther one searches back in time.
Older, more ancient rocks are poorly represented today. Therefore it is hard to clarify if an assemblage went extinct in a short interval or not.
It is not known for sure how many mass extinctions have occurred throughout history, but good evidence exists regarding the Phanerozioc era.
According to Steven Stanley
Changing Earth's albedo, and thus its solar budget, and thus its weather
Producing more continental climates in interiors, changing regional ecosystems
Change oceanographic conditions, by removing the once-vast epeiric sea systems and by removing a major source of productivity
Would operate over a 4 million year scale
1980: Walter Alvarez was investigating a layer of clay in Gubbio, Italy at the K/Pg boundary. Wanted to determine length of time represented by the clay layer. Consulted dad (Nobel winning physicist Luis Alvarez) for possible solution. Suggestion:
1. Meteors impact the Earth's atmosphere all the time2. Some chemical elements more common in meteors and such than on Earth's surface: these should be traceable in minute quantities in sediment3. Find the average infalling rate of these elements today; use this rate and observed amount at the Gubbio clay layer to find out how much time
Chances were that the impact was in ocean basins, but most Cretaceous ocean basins have been recycled by plate tectonics
Some early leads were in Siberia (too early); Manson, Iowa (too small and too early (within Late K))
Nearly all geological lines of evidence (tektites, tsunami deposits, ejecta deposits, shocked quartz, etc.) were more abundant in Western Hemisphere, and especially in the Gulf of Mexico, than the rest of the world: pointed to impact in that region!
In Yucatan, Mexico: disrupted layers at K/Pg boundary in buried rock Seismic and gravity scan suggested a crater 180 km across: the right size! Although not visible as a crater because buried under 300-1000 m of Cenozoic rock, it can be seen using sensitive satellite and other data
Crater was named Chicxulub, after nearby town
Quartz is one of the most common of all minerals
When subjected to intense heat & pressure, forms shock planes
Shocked quartz has been found in over 100 K/Pg boundary sites worldwide
Material thrown up by impact would melt during reentry, form glassy spheres
These have been found at some K/Pg sites
Animals with larger total food requirements die more those with less
In marine communities, foodwebs tied into photosynthesis (that is, direct from the phytoplankton) would be hit harder than bottom feeders (which feed on the accumulated decayed remains of organisms)
Additionally, taxa dependant on symbiotic algae would be devastated
Some geologic record other than just iridium might remain
Effects would be global and essentially instantaneous: hours to days to months to a few years
Thick units probably formed by tsunami found at K/Pg in Carribbean, Gulf Coast of Texas, Mexico, Central America, and South America
Thinner but widespread deposits of ejecta (material flung through the air) at K/Pg in Carribbean, Gulf Coast of Texas, Mexico, Central America, and South America
