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 have are now used as index fossils? *
A. They became extinct.
B. They changed their diets.
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C. They hid in marine sediments.
D. They migrated of new environment

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

idk what happened..you tell

answer; the code in musculoskeletal system subsection is associated with deep tissue possibly to the bone;