Upon what basis were the upper and lower boundaries of the Mesozoic Era defined?
A) dramatic changes in the color of the rocks from green to tan
B) major episodes of mountain building
C) abrupt changes in the types of fossils, representing mass extinctions
D) the discovery that a meteoroid impact may have killed the dinosaurs

Question

Quizplus · Accepted Answer

The upper and lower boundaries of the Mesozoic Era are defined by abrupt changes in the types of fossils found, which represent mass extinctions. These changes mark significant shifts in the Earth's biological history, including the mass extinction at the end of the Cretaceous period that led to the demise of the dinosaurs.

Upon What Basis Were the Upper and Lower Boundaries of the Mesozoic