You are the lucky student of a wacky professor who develops a time machine. he asks if you will test it with him. you get in and there is an immediate glitch–the date readout fails so that when you land you are not sure what era you are in. your professor begins to panic, but you see something that tells you are in the cenozoic era. which of the following could it be?
1) archaean eon2) cambrian period3) cenozoic era4) mesozoic era