Dinosaurs, birds, early mammals and plants were major life-forms that existed in
a. mesozoic era
c. cenozoic era
b. paleozoic era
d. devonian era

The greenhouse effect a. something that has occurred for millions of years b. an unnatural phenomenon caused by humans that maintains earths temperature range. c. the results of the differences in the angle of the suns rays d. an unnatural phenomenon that causes heat energy to be radiated back into the atmosphere