What explains why certain dead organisms in the past were not fossilized?

They may not have skeletons, their body/bones were destroyed underground, the earth around them wasn't the correct type of rock, etc.

Explanation:

Only a small percentage of organisms are ever fossilized, and can only be fossilized under specific circumstances.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]