How are catastrophic events related to changes in geological timelines? A. They aren't related to changes in the geological timeline because they don't change the
overall population dynamics.
B. They aren't related to changes in the geological timeline because the timeline is dictated
by temperature cycles.
C. They cause significant changes that disrupt the equilibrium of the earth and lead to
natural separation points.
D. They define geological periods because scientists use them as reference points for
tracking the history of the earth.
PLEASE ONLY ANSWER IF YOU KNOW-

D. They define geological periods because scientists use them as reference points for  tracking the history of the earth.

Explanation:

Catastrophic events related to changes in geological timeline are very useful in defining geological periods.

These events have very significant appearance in the geological record and can be used to determine the history of the earth.

The catastrophic events usually culminates into extinction cycles or termination of some organisms from the earth surface.

Geologists use these events that are often wide spread to delineate geological periods.

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b. lithosphere, asthenosphere, mesosphere   is the answer most likely