Life is challenging to define, but living beings breathe, move, sense, grow, reproduce, create secretions and nourish themselves; inanimates do not.

After the first few hundred million years of its birth, Earth cooled down enough for permanent oceans to form on its rocky surface. The atmosphere of the young planet was still toxic and blistering, but somewhere at the bottom of the oceans, the environment was suitable for organisms – life – to evolve.

Deep down in the water, molecules, inanimate by nature, began to form ever more sophisticated structures. They grouped into countless combinations until one, by sheer chance, formed a cell, the smallest unit of life that could grow and reproduce around 3.8 billion years ago.

What is life? It is hard to explain. There is no standard definition of life, but we can usually recognize living things when we see them. They typically breathe, move, sense, grow, reproduce, create secretions and nourish themselves. Plants and animals are the most familiar life forms for us.

At first, life consisted of just single-celled organisms, such as bacteria and archaea, living in oceans. Over time, organisms evolved into more complex forms consisting of more than one cell (e.g., a human consists of trillions of cells) – from oceans to ground, from ground to skies. Over billions of years, evolution has given birth to countless living species, many already extinct, many inhabiting our planet while many new are continuously evolving. We have named around two million species, knowing that this is only a tiny fraction of all life.

Life itself may look bewilderingly diverse, yet we all have one common ancestor, one of those single-celled organisms living billions of years ago. Hence, you might not be surprised to hear your genes¹ are 99% similar to chimpanzees, 80% to cows, 60% to bananas, and 50% to trees.

¹ Genes are an instruction manual for organisms - your body, for example. Genes define how your body is built, how it looks, and how it functions.

Bibliography

Rutherford, A. 2014. Creation The Origin of Life. London, United Kingdom: Penguin Books. 272 p. ISBN 9781780229072.

Panciroli, E. 2022. The Earth a Biography of Life The Story of Life On Our Planet Through 47 Incredible Organisms. London, United Kingdom: An Hachette UK company. 255 p. ISBN 9781529413984. Pages 18-19.

Bregman, R. 2022. Humankind a Hopeful History. Translated by M. Janatuinen. Helsinki, Finland: Otava. 441 p. ISBN 9789511424178. Pages 63-65.

Parker, S. 2019. A Short History of Medicine. London, United Kingdom: Penguin Random House. 400 p. ISBN 9780241379653. Pages 338, 341.

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