Across
1
Substance with pH above 7
3
Force that attracts objects together
5
Gas essential for breathing
6
Unit of energy
9
The Red Planet
13
Preserved remains of ancient life
Down
2
Element found in all living things
4
Unit of electric potential
7
Blocking of light by a celestial body
8
Our home planet
10
Curved glass that refracts light
11
Molten rock beneath Earth surface
12
Nerve cell in the brain