Everything Life Sciences Grade 10

Causesof mass extinctions DUMMY

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

Impact event

The impact of an asteroid smashing into Earth may have caused food chains to collapse both

on land and at sea producing toxic gases blocking out sunlight and preventing photosynthe-

sis. The impact also resulted in the production of sulfur rich acid rain, caused forest fires and

mega-tsunamis. Scientists believe that an asteroid was responsible for the mass extinction 65

million years ago, producing the 600 km crater found in India.

Volcanic activity

Some scientists, using dating technology and other methods, 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.

Figure 11.14: Deccan traps, Mahabaleshwar, India.

332 11.4. Mass extinctions