BISC 100 Lecture Notes - Lecture 9: Ocean Acidification, Marine Life, Introduced Species
7 Mar 2020
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BISC 100 EVOLUTION/DIVERSITY PART 3
The “Big Five” Mass Extinction Events
▪ In each of the five mass extinction events, 50% or more of marine species became extinct
▪ The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras 252
million years ago
▪ This mass extinction occurred in less than 500,000 years and caused the extinction of about
96% of marine animal species
▪ A number of factors might have contributed to this mass extinction
▪ Extreme volcanism in what is now Siberia
▪ Global warming and ocean acidification resulting from the emission of large amounts of
CO2 from volcanoes
▪ Anoxic conditions resulting from nutrient enrichment of ecosystems
▪ The Cretaceous mass extinction occurred 66 million years ago
▪ More than half of all marine species, many families of terrestrial plants and animals, and all of
the dinosaurs, except birds, went extinct during this event
▪ The presence of iridium in sedimentary rocks from that time period suggests a meteorite impact
▪ Dust clouds caused by the impact would have blocked sunlight and disturbed the global climate
▪ The Chicxulub crater off the coast of Mexico is evidence of a massive meteorite collision that
dates to the same time
Is a Sixth Mass Extinction Under Way?
▪ Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical
background rate seen in the fossil record
▪ It is difficult to estimate current extinction rates because many undiscovered species may be
lost through destruction of the tropical rain forest
▪ Many species are declining rapidly due to habitat loss, introduced species, overharvesting, and
other factors
▪ Climate change may hasten declines; extinction rates historically have tended to increase when
global temperatures were high
▪ Data suggest that a sixth, human-caused mass extinction is likely to occur unless dramatic
action is taken
Consequences of Mass Extinctions
▪ It typically takes 5–10 million years for diversity to recover following a mass extinction; in
some cases up to 100 million years
▪ Mass extinctions can change the types of organisms found in ecological communities
▪ For example, the proportion of predators increased in marine communities after the
Permian and Cretaceous mass extinctions
▪ Mass extinctions can also eliminate lineages with novel and advantageous features
Document Summary
96% of marine animal species: a number of factors might have contributed to this mass extinction, extreme volcanism in what is now siberia, global warming and ocean acidification resulting from the emission of large amounts of. Is a sixth mass extinction under way: scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate seen in the fossil record. Permian and cretaceous mass extinctions: mass extinctions can also eliminate lineages with novel and advantageous features, for example, shell-drilling gastropods were lost in the extinction at the end of the. Triassic and did not reappear for 120 million years. Evolution is not goal oriented: evolution is like tinkering it is a process in which new forms arise by the slight modification of existing forms. Linking classification and phylogeny: the evolutionary history of a group of organisms can be represented in a branching phylogenetic tree.
