Across
1
Smallest unit of an element
3
Nerve cell in the brain
6
Preserved remains of ancient life
7
Blocking of light by a celestial body
10
Group of similar cells
12
Icy body with a tail near the sun
Down
1
Substance with pH below 7
2
Second lightest element
4
Form of thermal energy
5
Mass per unit volume
6
Push or pull on an object
8
Magnetic metallic element
9
Center of an atom or cell
11
Tectonic landmass section