1. What is Mass Extinction?
A mass extinction occurs when a large fraction of all living species becomes rapidly extinct.
The fossil record shows that at least five major mass extinctions have occurred in the past 500 million years.
Impacts of asteroids on Earth are suspected as a primary cause of mass extinction.

2. Percentage of families that went extinct
Mass Extinction 60 40
Percentage of families that went extinct 20
500
400
300
200
100
Time (millions of years ago)

3. 1.The Ordovician Extinction
Since more water was in ice form, the sea level lowered all over the world, causing a reduction of space for life on continental shelves.
The most affected animal group was the marine invertebrates, in which more than 100 families were wiped out.
This extinction occurred at end of the period, about mya.
It is thought to be caused by a global cooling, which caused the continent Gondwana to glaciate. Geologists have found glacial deposits in the Saharan desert, which provided the evidence for this theory.

4. The species that survived the Ordovician extinction rediversified during the Silurian and Devonian periods.
Sharks made their first appearance during this time, and reef-builders such as coral were flourishing in the oceans.
The first land plants were forming, which allowed forests to arise.
Other new species included amphibians and insects.

5. 2. Devonian Extinction (~350mya)
This event is theorized to be caused by an episode of global cooling similar to that of the Ordovician extinction.
This time, the glacial deposits have been found in northern Brazil.
However, meteorite impacts have also been thought a possible cause of this mass extinction, although the evidence remains inconclusive.
This extinction had little effect on land animals, mostly affecting (again) the marine life, in particular, the reef-builders.

6. The Permian Extinction
At the end of the Permian period (about 245 mya), the most severe mass extinction occurred, wiping out 90-95% of marine and 70% of land species.
Many theories of what caused this extinction have been considered:
The glaciation of Gondwanaland, the primary theory for the two previous mass extinctions,
the increased fluctuation of global temperatures caused by north and south pole glacier events,
volcanic eruptions occurring in Siberia, and
The formation of super-continent Pangaea, which possibly caused a reduction of space on the continental shelf.

7. The Permian Extinction’s Effects
The main effect of this mass extinction was the increased number and variety of reptiles, both on land and in the ocean.
This made way for what has been called the “age of the dinosaurs,” because it helped to wipe out competing species.

8. Triassic-Jurassic Extinction (~200mya)
During the Triassic period, there was a super continent call Pangaea.
In the mid-Jurassic period, Pangaea broke apart into Laurasia and Gondwanaland
Volcanic eruptions and the split of Pangaea caused another mass extinction
The continental drift was accompanied by volcanic activity and continued during the Cretaceous period at a fast pace.

9. K-T Extinction
The K-T impact caused the extinction of many species including the dinosaurs and 60-80% of life at that time.
Sudden extinction thought to be caused by an asteroid “Impact Hypothesis”
In 1980, Walter Alvarez of U of California at Berkeley found a layer of iridium in sediments that dated from the time of the K-T extinction.

11. Impact site

12. Greenhouse Earth, Icehouse Earth, and sea level change
Greenhouse Earth: when there is little to no ice on Earth including on the Polar Ice Caps. The temperatures are very high
Icehouse Earth is when worldwide temperatures are very low.
Scientists are scared that there will be no ice on Earth because sea level will rise.

13. Sea Level Changes
During the beginning of the Cretaceous period, global sea levels were really high because there was no polar ice. Later in this period, the sea levels dropped. Because the climate cooled off tremendously, many animals were driven to extinction but unique dinosaurs were able to evolve on different continents.
During the Tertiary period of the Cenozoic era, extreme cooling occurred. But during the Quaternary period, cooling continued resulting in a series of ice ages. This cooling led to the high rates of evolution and extinction among mammals.

16. Diversification and Speciation after Mass Extinction
Surviving Species take over vacant habitats and resources
Speciation takes every 100 to 100,000 year
10 to 10,000 new species per year
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

17. PERIOD
ONSET
MAJOR EVENTS ME
Paleozoic
Cambrian
540 Ma
most animal phyla present, diverse algae
Ordovician
490 Ma
first jawless fishes, animal diversification
1st
Silurian
445 Ma
first bony fishes, colonization of land
Devonian
420 Ma
first insects and amphibians, fish diversify
2nd
Carboniferous
355 Ma
extensive forests, first reptiles, insects radiate
Permian
290 Ma
reptiles radiate, insects are diverse
3rd
Mesozoic
Triassic
250 Ma
early dinosaurs, first mammals, marine inverts. diversify
4th
Jurassic
200 Ma
first birds, diverse dinosaurs
Cretaceous
145 Ma
flowering plants and mammals diversity, dinosaurs continue diversification
5th
Cenozoic
Tertiary
65 Ma
radiation of mammals, birds, flowering plants, pollinating insects
Quaternary
2 Ma
humans evolve, extinctions of large mammals

18. Is there a potential Sixth Major Extinction
Is there a potential Sixth Major Extinction? Species are becoming extinct at a rate of about 4000/year 100/day 1species every 15 minutes
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

19. 2050
50% of all species on the planet will be either endangered or extinct
Habitat destruction
Global Warming
25% mammalian species
15% bird species
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.