1 Early theories about life
1.1 Materialism
1.2 Hylomorphism
1.3 Vitalism
2 Definitions
2.1 Biology
2.2 Biophysics
2.3 Living systems theories
3 Origin of life
4 Conditions for life
4.1 Range of tolerance
4.2 Extremophiles
5 Classification of life
6 Extraterrestrial life
7 Death
7.1 Extinction
7.2 Fossils