Question

Earth's Mass Extinction Events



Through analysis of the fossil record, scientists have determined that Earth has experienced at least five mass extinction events. The timeline describes these five events.



Extinction event 1 occurred 445 million years ago during the ordovician period. It was likely caused by an intense ice age and 60 to 70% of global species went extinct. Extinction event 2 occurred 375 to 360 million years ago during the devonian period. It was likely caused from oxygen depletion in the oceans and 75% of global species went extinct. Extinction event 3 occurred 252 million years ago during the permian period. It was likely caused from asteroid impacts and intense volcanic activity and 95% of the global species went extinct. Extinction event 4 occurred 200 million years ago during the triassic period. The cause is debated but likely from massive volcanic eruptions and asteroids and 70 to 80% of the global species went extinct. Extinction event 5 occurred 66 million years ago during the cretaceous period. It was likely caused from an asteroid impact and 75% of the global species went extinct.



Which TWO are true of the mass extinction events from the passage?


All life on Earth was destroyed during each event.


All the extinction events were caused by asteroid impacts.


The events were caused by changes to Earth's environment.


Intense ice ages had the greatest impact on species extinction.


At least 50% of the species on Earth were destroyed during each event.

Answer 1

- The events were caused by changes to Earth's environment.
- At least 50% of the species on Earth were destroyed during each event.

(Each listed event cites environmental causes—ice age, ocean oxygen depletion, asteroid impacts, volcanic activity—and all given extinction percentages are ≥50%.)