Across
1
Second lightest element
2
Molten rock beneath Earth surface
4
Blocking of light by a celestial body
5
Gas essential for breathing
8
Positive particle in nucleus
11
Preserved remains of ancient life
13
Infectious microscopic agent
Down
2
Tissue that contracts for movement
3
Unit of energy
6
Precious yellow metallic element
7
Compound containing oxygen
8
Particle of light
9
Chemical element in table salt
10
Fourth state of matter
12
Center of an atom or cell