Mass Extinctions Flashcards
What is a mass extinction?
It is when many species die out over the same period of time
How many mass extinctions have occurred since the creation of life on earth?
Five
What are the five major mass extinctions?
End of Ordovician period Late Devonian period End of Permian period End of Triassic period End of Cretaceous period
When did the mass extinction at the end of the Ordovician period occur?
435 mya
What is special about the mass extinction at the end of the Ordovician period?
It is the second biggest mass extinction
What was a possible cause of the mass extinction at the end of Ordovician period?
Climatic changes (ice age, with a possible drop in sea level)
When did the mass extinction during the late Devonian period occur?
345 mya
What caused the mass extinction late in the Devonian period?
The exact cause is unknown
It may have been an ice age with a drop in sea level
When did the mass extinction at the end of the Permian period occur?
250 mya
What caused the mass extinction at the end of the Permian period?
Climatic changes Ice age Volcanic eruptions Flood Comet or asteroid
What was special about the mass extinction at the end of the Permian period?
It was the biggest mass extinction in history
About 90% of all life on earth was wiped out
When did the mass extinction at the end of the Triassic period occur?
190 mya
What caused the mass extinction at the end of the Triassic period?
It is uncertain
Could have been global warming, ice age or volcanic eruptions
What happened after the mass extinction late in the Devonian period?
Amphibians became terrestrial
What happened after the biggest mass extinction?
Reptiles replaced huge amphibians as the dominant group
What was life like before the mass extinction at the end of the Ordovician period?
Until this time, life was limited to the water, with very little life on land
What is special about the mass extinction at the end of the Triassic period?
The last of the big amphibians became extinct
What happened after the mass extinction at the end of the Triassic period?
Dinosaurs were abundant
When did the mass extinction at the end of the Cretaceous period occur?
65 mya
What caused the mass extinction at the end of the Cretaceous period?
Possibly a meteorite collision with the earth
Volcanic eruptions
Why do scientists think that a meteorite collision caused the mass extinction at the end of the Cretaceous period?
The Yucatan Peninsula seems to show evidence of the collision
What is special about the mass extinction at the end of the Cretaceous period?
The dinosaurs became extinct
Marine ammonites became extinct
What happened after the mass extinction at the end of the Cretaceous period?
Mammals increased and became the dominant group
Why do scientists suspect volcanic eruptions caused the mass extinction at the end of the Cretaceous?
There is evidence of a high level of volcanic activity at that time
Where was the main concentration of these volcanic eruptions?
In the Deccan region of India
What probably caused this raised level of volcanic activity?
India was a separate mass of land drifting north
The collision with Asia probably caused it
Why could volcanic activity cause a mass extinction?
Dust and ash released into the air could block out the sun’s rays
This led to a cooling of the atmosphere
Ice sheets were formed at the poles, sea levels dropped and the aquatic habitats decreased
Less photosynthesis occurred
O2 in the atmosphere decreased
The surface of the earth becomes submerged in CO2
This intensifies global warming (greenhouse effect)
Ice masses melt
Terrestrial habitats are flooded and destroyed
What is a meteorite?
Mass of dust and rock moving through space
What is an asteroid?
A meteorite with a diameter of more than one kilometre
What is the asteroid impact theory?
A theory which speculates that the mass extinction at the end of the Cretaceous period was caused by an asteroid impact
Why would an asteroid cause a mass extinction?
Dust and rubble would have been released into the air
It blocked the sun’s rays, which could ave caused an ice age
The heat of the impact would have led to the extinction of many plant and animal species including the dinosaurs
Organisms could not adapt to the ch aged environment and died out
Photosynthesis stopped:
Plants became extinct
When this food source was lost, many other animals died out
O2 levels dropped
What other disasters would an asteroid impact have caused?
Worldwide fires
Huge tsunamis
Acid rain
Why do some scientists say that modern time is the sixth mass extinction?
The present rate of extinction is higher than any during any time in the past
How many species become extinct each year?
About 40 000
What is the cause of this “sixth mass extinction”?
The negative impact of humans on the environment
What is unique about this sixth mass extinction?
It is the only one with a biotic cause
