Mass Extinctions in the Past

There are many times in the geological record when there were massive extinctions of species. This figure has data for the number of families of species for different periods of geological time.

Note the large extinctions between the three major geological eras. The major extinction between the Mesozoic and Cenozoic eras is believed to be due to an asteroid that hit the earth about 65 million years ago.

• Where did this asteroid that hit the earth 65 million years ago land?
• Approximately how many species are represented by these families that became extinct 65 million years ago?

From your research you should be able to answer these questions:

• How many times have asteroids been implicated in the extinction of species?
• How often do asteroids pose a potential threat to the earth?
• How often has the earth been hit by interplanetary debris in the last 10 years?
• When an asteroid hits the earth, why do terrestrial species become extinct? (You should be able to come up with at least 3 ideas.)
• When an asteroid hits the earth, why do oceanic species become extinct? (You should be able to come up with at least 3 ideas.)
• The diagram for the geological record is for the number of families known at certain times during the earth's history. Because species are found within families, how many species do you think became extinct 65 million years ago?
• Do you think that there is any reason to believe that human treatment of the environment may accelerate the loss of species and add to a mass extinction? Defend your answer.
• List at least 7 reasons why species are becoming extinct.