You are the lucky student of a wacky professor who develops a time machine. she asks if you will test it with her. you get in and there is an immediate glitch - the date readout fails so that when you land you are not sure what eon/era you are in. as your time machine lands, you see an unusual landscape before you. as you open the door you realize you cannot breathe. you quickly shut the door, realizing you are in the
1) archaean eon2) cambrian period3) cenozoic era4) mesozoic era

1) Archaean eon

Explanation:  

Archaean eon  -

During the Archaean eon about 3.8 billion years ago, the earth's atmosphere was three times hotter than today's atmosphere. Earth's atmosphere was mainly more carbon dioxide and none of the Oxygen was in the atmosphere. In Archaean eon sedimentary rocks, stromatolites and first one-celled organisms appeared.

During Cambrian period sudden increase in diversity of many animal phyla was observed.

In Cenozoic era extinction of dinosaurs and rise of earliest homo sapiens has seen.

1) Archaean eon

Explanation:

In this geological period there is a report that the availability of atmospheric oxygen was very low or almost zero. In this era, photosynthesis was initiated and with it the production of oxygen as a waste substance of this process, however, being the levels probably at only 1% to 2% of its current level would not allow a human of this time to breathe.

most community's take hundreds of years to become stable