Until the , only one-celled organisms lived on land, but during this period, plants became abundant.

The answer is Silurian period (443 million to 416 million years ago). This was the era when life in the seas and oceans began to conquer land. This is associated with a period of warm climate, rising sea and ocean levels hence giving shallow-water grounds where reefs developed. Plants like bryophyte began to develop including the emergence of terrestrial arthropods

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.

this is more of a statement than a question. is there answers to go along with this, or is it opinion based?