Cyanobacteria dramatically changed the composition of life forms on Earth by leading to the near-extinction of oxygen-intolerant organisms.

123 definitions?!

Scientists and philosophers have compiled at least 123 definitions of life. Many now argue life is a process, not a substance.

Life: Why Defining It Is So Hard

A vibrant green fern leaf on a dark background, perfect for nature-themed wallpapers.

The working checklist

Biologists use traits—from homeostasis to reproduction—to spot life in action.

Life: Why Defining It Is So Hard

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