Causes of Mass Extinctions
Causes of Mass Extinctions
Watch a video about the debate about what really killed the dinosaurs.
There is still a lot of debate among scientists as to what caused the mass extinctions. To be a valid theory to explain what caused mass extinctions, the theory must:
- explain all the losses of species at a particular mass extinction event (not just specific losses e.g. dinosaurs).
- explain why some organisms died and others survived.
- be based on natural events and processes that are shown to have occurred around the time of extinction.
Two of the hypotheses put forward are:
- the impact theory of extinction
- massive volcanic activity
Watch a video about the meteor impact that may have caused the extinction of the dinosaurs.
Impact event
Scientists believe that an asteroid was responsible for the mass extinction that occurred 65 million years ago. The meteorite that hit Earth was most likely 10 km in diameter, and upon impact it would have released an amount of energy that was 2 million times more powerful than the most powerful man-made device ever created. The massive impact caused earthquakes and volcanic eruptions that produced toxic gases, and ejected dust, soot and debris into the air, blocking out sunlight and preventing photosynthesis. The impact also resulted in the production of sulfur rich acid rain and caused forest fires and mega-tsunamis. The impact of an asteroid smashing into Earth may have caused food chains to collapse both on land and at sea. They believe this impact produced the 180 km wide Chicxulub crater found in the Gulf of Mexico.
Illustration of an impact event.
Volcanic activity
Some scientists believe that volcanic eruptions may have caused the mass extinction event at the end of the Cretaceous period that led to the extinction of among others, the dinosaurs. The researchers, through examining a trail of dead particles floating in the sea, spanning half a million years, developed a timeline that links mass extinction to large-scale eruptions of the Deccan Traps, an ancient volcanic range in Western India. Evidence suggests that the massive volcanic eruptions pumped out massive quantities of carbon dioxide and sulphur dioxide into the air, thus altering the climate and contributing to the mass extinction event at the end of the Cretaceous period.
Deccan traps, Mahabaleshwar, India.
Optional Activity: What caused the mass extinctions?
Aim
To use understanding of fossil evidence and scientific method to demonstrate how each of the hypotheses for mass extinction arrives at its conclusion.
Instructions
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What are the key requirements of a theory that attempts to explain the mass extinctions?
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Choose one of the two hypotheses discussed and describe it in your own words. List the evidence that supports the theory.
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Through your research on the Internet and by reading books in the library, list any other evidence that you found in support of your chosen hypothesis.
This lesson is part of:
History of Life on Earth