Basis of biostratigraphic zonation (changes of organisms through time)

Basis of biostratigraphic zonation
(changes of organisms through time)

Individuals of the same species don’t have equal ability to survive in the environment. These variations arise by chance. Successful variations help organisms survive and extend their environment and range. Unsuccessful variations result in extinction.

This process of weeding out the unfit and survival of the fittest is termed Natural selection. These favorable variations are inheritable and can be transmitted from one generation to the next. New species appear as a result of that, where individuals that undergo favorable adaptations will stand a better chance surviving and reproducing. Spontaneous changes in genes are called mutations.

The basis of biostratigraphy depends on the fact that species don’t remain immutable for all time. If environmental conditions remained absolutely constant through time, perhaps species would never change. Because environments change, species also change although environments don’t directly cause species to change.

Both gene mutation or gene pool combinations and shifting environmental conditions are essential to the evolution of species.

Species variations are one-directional and nonreversible. Once a species has become extinct, it doesn’t reappear in the fossil record.

As members of a new species increase in numbers and eventually become abundant they record their first appearance. When the species is no longer able to adjust to shifting environmental conditions, its members decrease in number and eventually disappear (become extinct), this is the last appearance of species.