Question

if sill f in question #43 intruded 428 million years ago, in which era did it form?
○ mesozoic
○ paleozoic
○ cenozoic
○ precambrian

Explanation:

The Paleozoic era lasted from about 541 to 252 million years ago. Since 428 million years ago falls within this time - frame, the sill formed in the Paleozoic era. The Mesozoic era was from about 252 to 66 million years ago, the Cenozoic era from about 66 million years ago to the present, and the Precambrian is the time before the Paleozoic, ending about 541 million years ago.

Answer:

Paleozoic