What gas did not appear in any measurable amount until about 2.0 BY BP?

The correct answer is Oxygen.

Explanation:

2.0 BYBP means 2 billion year before present.

The theory of evolution holds that the the synthesis into primitive life forms of the basic chemical components of life such as carbon, nitrogen, hydrogen and oxygen occurred in an atmosphere without any oxygen.

The presence of oxygen in our plant today is explained by two processes.

They are:

The process of Photosynthesis which is the chief contributor of oxygen to the earths atmosphere is said to have spanned billions of years.

Cheers!

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.