Across
1
Path of a planet around the sun
2
Basic unit of life
5
Molten rock beneath Earth surface
7
Measure of matter in an object
8
Particle of light
10
Nerve cell in the brain
Down
1
Gas essential for breathing
3
Form of thermal energy
4
Element found in all living things
5
Natural satellite of Earth
6
Curved glass that refracts light
9
Unit of power
11
Preserved remains of ancient life