Which highly reactive gas was probably absent from the earth's primitive atmosphere?

Significant figures are digits read directly from the measuring instrument plus one more digit, which is __ by the observer.

Which process does not require the presence of a physical substance in order to transfer heat? air in the atmosphere is heated by the ground. this warm air then rises, and cooler air falls. this is an example of what type of process? how is conduction different from radiation?

Which three statements represent the benefits of performing experiments using computer simulations?