Q: An estimated 99 percent of the species that have ever lived on earth no longer exist, showing that what event is common?


Read this paragraph and choose the correct option from the provided answers:

Even though large life forms have been very successful on Earth, most of the life forms on Earth today are still prokaryotes—small, relatively simple single-celled organisms. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; in fact, it is estimated that 99% of the species that have ever lived on Earth no longer exist.

 Choices:

- accumulation

- over fishing

- pollution

- extinction


A:
extinction