What are the 4 states of matter?

Can you give me more detailed information on the 4 stages of matter, especially plasma? What is plasma? Where does it come from?

What are density and specific gravity?

What is the best estimate of the densities of the various layers of the Earth?

How have scientists discovered the density of the earth?

 What is bedrock?

Can you please tell us where on earth that the "earth's crust" can be seen?

What's in the center of the earth?

What are density and specific gravity?

How have scientists discovered the density of the earth?

What is Differentiation?