Where do short-period comets (those with an orbital period of 200 years or less) originate?

Which of the following statements is true about the Earth’s crust?   I. It “floats” on the mantle.   II. It constitutes less than 1% of the Earth’s mass.   III. It has an average density of 2.8 g/cm3.

Under the proto-planet nebular model, why are the four inner planets terrestrial (rocky) instead of gas giants?

What is the name that geologists assign the premise that the present is the key to understanding the past?

What is the name assigned to a time break in the rock record?

A river with a very slight gradient, levees, and numerous oxbow lakes is in which stage of its lifecycle?

Why are the alignments that result in solar and lunar eclipses so rare?

Which atmospheric layer reflects radio waves?

Who first proposed the “super continent” of Pangaea?

Small changes that result in the breaking up, crumbling, and destruction of any kind of rock are