Question

which eon spans from 540 million years ago to the present day?
precambrian
paleozoic
phanerozoic
cenozoic

Explanation:

The Phanerozoic Eon started about 541 million years ago and continues to the present. The Precambrian is a supereon that ended about 541 million years ago. The Paleozoic is an era within the Phanerozoic (from about 541 - 252 million years ago). The Cenozoic is also an era within the Phanerozoic (from about 66 million years ago to present).

Answer:

Phanerozoic