During which geologic epoch do scientists infer

that the earliest grasses first appeared on Earth?

(1) Holocene

(2) Pleistocene

(3) Oligocene

(4) Eocene

Grasses evolved around 40 million years go, that is in the Paleogene period.

Paleogene can be divided into Oligocene, Eocene and Paleocene.

40 Millions years ago falls into Eocene - this is the correct answer.

Grasses actually appeared rather late, and other plants, including ones with flowers appeared earlier.