Which process always causes a profile to become thinner index fossils?

The process of compression always causes a profile to become thinner index fossils.

Explanation:

When a fossil is subjected to increasing pressure over years of development of layers of earthly material over it, it automatically undergoes compression and is shrunk down to become a thinner index fossil. Once the fossil undergoes the process of compression, it becomes extremely hard to excavate it. These unexcavated fossils later undergo the process of mineralization and get converted into certain minerals of usually untraceable origin.

Answer barren with few trees, in the northern hemisphere;

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