Across
1
Preserved remains of ancient life
3
Smallest unit of an element
4
Center of an atom or cell
6
Substance with pH below 7
9
Tectonic landmass section
Down
2
Mass per unit volume
5
Group of similar cells
7
Disturbance that transfers energy
8
Measure of matter in an object
9
Particle of light
10
The Red Planet