Across
1
Fourth state of matter
5
Center of an atom or cell
6
Our home planet
10
Icy body with a tail near the sun
11
Magnetic metallic element
Down
2
Mass per unit volume
3
Preserved remains of ancient life
4
Amplified beam of light
7
Compound containing oxygen
8
Natural satellite of Earth
9
Nerve cell in the brain
12
Naturally occurring inorganic solid