Larger organisms, mainly eukaryotes, can consist of single cells or may be multicellular with more complex structure. Life is only known to exist on Earth but extraterrestrial life is thought probable. Artificial life is being simulated and explored by scientists and engineers.
The phenomenon of life can be approached in several ways: life as it is known and studied on planet Earth; life imaginable in principle; and life, by hypothesis, that might exist elsewhere in the universe (see extraterrestrial life).
The diversity of life on Earth is a result of mutations or random changes in hereditary material over time. These mutations allow the possibility for organisms to adapt to a changing environment.
Defining life from the viewpoint of examining its characteristics reveals how much life on Earth has in common, and helps distinguish between living and non-living things.
Science Daily: Meteor impacts may have sparked life on Earth, scientists say
Asteroid impacts may have helped kick-start life on Earth by creating hot, chemical-rich environments ideal for early biology. These impact-generated hydrothermal systems could have lasted thousands ...
Phys.org: Impacts from meteors may have helped start life on Earth by creating hydrothermal vents
Meteor impacts may have helped spark life on Earth, creating hot, chemical-rich environments where the first living cells could take shape, according to research integrated by a recent Rutgers ...
Impacts from meteors may have helped start life on Earth by creating hydrothermal vents
The Conversation: How do we understand life on Earth? A prize‑winning biography charts the tension between two types of science ‘genius’