Why are time periods in the geologic time scale are not even in length? They are based on the type of fossils found in rock layers of the earth.

They are based on a different type of calendar used to track Earth's history.

They are baed on the thickness of the Earth's rock layers.

They are based on important events happened in Earth's history.

Here is a picture  of the net. its 4 squares in a row diagonal and on the third draw one square aove and under

To relate to humans in a relational humanly way. 

Your answer is d. silli hope this ! : ) i left an explanation down below if you need it: a sill forms when hot magma squeezes between layers of rock to form a hardened sheet of rock. a sill is basically a tabular sheet intrusion between old layers of sedimentary rock, volcanic beds, or in the direction of foliation inherent in metamorphic rock. the word sill means a concordant intrusive sheet.