which gas is inferred to have been absent from
earth's atmosphere during the early archean
eon?

Free Oxygen  is inferred to have been absent from  Earth's atmosphere during the Early Archean  Eon.

Explanation:

During the early Archean Eon the free Oxygen was found to be absent. Though water molecules were found and the water molecules contained Oxygen it was found combined with the Hydrogen molecule not as free Oxygen.

Due to the absence of Oxygen only blue green algae was found. But they started to release Oxygen as a waste product. Eventually the Oxygen started to infer into the atmosphere. Due to organic photosynthesis Oxygen accumulated in the atmosphere .

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.