When dead animals break down, which of the following is released into the atmosphere? calcium, carbon dioxide, oxygen, greenhouse gase

carbon dioxide

Explanation:

when   animal dies their bodies get decayed by the actions of natural recyclers called decomposers e.g bacteria, worms, slugs.  most of the carbon they consumed while still alive is exhaled as carbon dioxide, and when the animal eventually dies the natural recyclers called decomposers  returns the carbon in their body back to the atmosphere in the form of carbon dioxide.

so therefore , when dead animals break down carbondioxide is released into the atmosphere.