What subspecialty of Earth science studies ancient environments?

Paleontology.

Explanation:

Paleontology comes under the rubric of the study of Earth sciences. Paleontology is that subspeciality that studies the ancient environments of Earth. Paleontologists studies the history of earth by studying the fossils, that is the remains of plants, animals, bacteria, etc.

These fossils are usually buried under rocks. This science of study lies somewhere between geology and  biology. It studies how humans evlved as species.

An example of paleontology study is the study of Neanderthals, an extinct species of early humans.

Thus the correct answer is Paleontology.

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