Sesamoid bones occurring in some tendons function to

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.

Can someone give me the answer to this question? you so much