Mass Extinctions

Extinctions

• extinctions are a recurring theme over the history of life on Earth

• 99% of species that have ever lived on Earth have gone extinct (extinctions are very common)

• extinction operates at a fairly constant rate, culling some species while speciation generates new ones = background extinctions

Mass Extinctions

• those that far exceed the rate of speciation

What is a Mass Extinction Event?

1. at least 30% of species lost

2. broad range of ecologies

3. short/sudden (geologically speaking — which is still hundreds of thousands of years)

The Geological Timescale

• dividing the 4.6 billion years of Earth’s history into time periods

  • determined by fossil records and dating with isotopes

• many of these major divisions based on extinction events

• the base of new periods defined on the RADIATION of new species

  • foraminifera ranges fossils — extinction and radiation of new species used to determine end of cretaceous and start of paleogene

5 Mass Extinctions

1. End - Ordivician

2. End - Devonian

3. End - Permian

4. End - Triassic

5. End - Cretaceous

End - Ordivician Extinction

• devastates marine invertebrates

End - Devonian Extinction

• devastates reef-building organisms

End - Permian Extinction

• devastates trilobites, pelycosaurs, placoderms

• largest mass extinction event

End - Triassic Extinction

• devastates conodonts and large amphibians

End - Cretaceous Extinction

• devastates non-avian dinosaurs, pterosaurs, ammonites, and many plants

Importance of Extinctions

• “opens up evolutionary pathways by freeing ecological space.” Stephan J. Gould, 1985

• extinction of dinos made space for mammals (they existed before but not as large or as many)

What Causes Mass Extinctions

1. Biological

   • competition

   • predation

   • pathogens

     • evidence that this was involved in some mass extinction events

2. Earth Based

   • changes in continental configuration:

     • changes in climate/sea level

       • ex; Late Ordovician Extinction — loses primarily in ocean even though changes were on land

     • The greater the landmass the lower the diversity — because life tends to be really diverse around continental shelves (on the edge)

       • more smaller, broken up continents = more surface area in shelves for diversity

       • ex; End Permian Extinction

   • Atmospheric — Volcanism

     • greenhouse/cold house effects

3. Extraterrestrial

   • lots of evidence for this occurring at the end cretaceous extinction

4. Combination of many factors

Evidence for Mass Extinction Events

• the rock record!

  • rock layers around the extinction are noticeably different in their compositions — showing the effects of environmental disturbances that triggered the mass extinction

• the fossil record!

  • older rock layer contains a great diversity of fossil life forms, while the younger layer immediately above is depauperate in comparison

6th Mass Extinction

• the changes humans have made to the Earth are disrupting its systems at global scales

  • biological cause → direct result of changes humans have made

• extinction rates have risen drastically over the last 500 years

• we are currently losing species hundred of times faster than normal background extinction rates

The Good News about the 6th Mass Extinction

• “The past is the key to the present”

  • investigating Earth’s past extinctions may be one of the keys to preserving biodiversity for the future

• previous mass extinctions have been caused by factors entirely out of our control: asteroid impacts, volcanic activity, etc.

• since we are causing this, we can also stop it: YOUR actions make a difference

  • VOTE for politicians and parties that have significance policies surrounding climate change and biodiversity loss

  • CONSUME LESS (less power, less gas, buy less stuff, buy sustainable products, eat less or no meat, boycott companies that pollute)

  • make good CHOICES!