PLS ANSWER QUICK Index fossils help scientists estimate the age of a rock because index fossil species only existed for a relatively short time. What happened to the species that are now used as index fossils.
1. They became extinct
2.They changed diets
3.They hid in marine sediments
4.They migrated to new environments

They became extinct.

Explanation:

The text says that index fossil species only existed for a relatively short time. If they don't exist anymore, that means that they are extinct.

1. They became extinct

they became extinct and lived for a distinct period of time which means that and sediment/ fossils found alongside these index fossils would be from the same time period

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex