Origins of Life on Earth (College Board AP® Biology): Study Guide

Evidence for the origins of life on Earth

• These hypotheses provide scientific explanations for how life may have originated on Earth

Geological evidence

• Earth formed around 4.6 billion years ago (bya) and remained too hostile for life until 3.9 bya

• Earliest fossil evidence of life dates to 3.5 bya, suggesting a plausible time range for life's origin

Organic molecules

• Organic monomers, e.g. amino acids and nucleotides, formed from inorganic molecules

• These monomers joined to form polymers capable of replication, and storing and transferring information

  • The Oparin-Haldane hypothesis suggests that life arose from inorganic precursors under early Earth conditions

    • The Miller-Urey experiment simulated primitive Earth, showing that organic molecules could form from inorganic compounds

  • The extra-terrestrial origin hypothesis states that organic molecules may have arrived via meteorites, such as the Maribo meteorite, which contained early organic matter

RNA world hypothesis

• This hypothesis proposes that RNA was the first genetic material

• RNA can store genetic information and catalyze chemical reactions, meaning that it could have enabled early life processes

• Modern ribosomes and self-replicating RNA support this theory

LUCA (Last Universal Common Ancestor)

• Fossil and genetic evidence suggest LUCA may have lived in hydrothermal vents, using chemosynthesis for energy

• Likely characteristics of LUCA:

  • anaerobic; it survived without oxygen

  • hydrogen was the energy source

  • CO₂ was converted into glucose

  • survived in extreme heat (thermophilic)