Origin of Life

About this topic

Earth formed about 4.6 billion years ago, and the earliest evidence of life is about 3.5 billion years old, as microfossils and stromatolites. The Miller–Urey experiment showed that organic molecules like amino acids can form from simple gases under lightning. The RNA world hypothesis suggests RNA was the first self-replicating molecule.

Early cells were prokaryotes; cyanobacteria later produced oxygen, changing the atmosphere. Eukaryotes arose through endosymbiosis about 2 billion years ago, and multicellular life later.

In 1953 Miller and Urey passed sparks through a mix of methane, ammonia, hydrogen and water, and made amino acids within days. Other ideas involve deep-sea hydrothermal vents, which supply energy and minerals, and clay surfaces. The RNA world hypothesis suggests that RNA, which can both store information and speed up reactions, came before DNA and proteins.

The first cells were probably simple prokaryotes living without oxygen; about 2.4 billion years ago cyanobacteria released oxygen by photosynthesis, which transformed the atmosphere and led to aerobic life. Eukaryotes appeared later through endosymbiosis. Students sometimes think life began from nothing suddenly; scientists see it as a gradual chemical process, but this is still an area of active research with open questions.