KEY CONCEPT Single-celled organisms existed 3.8 billion years ago.

1
KEY CONCEPT Single-celled organisms existed 3.8
billion years ago.
2
Microbes have changed the physical and chemical
composition of Earth.

• The oldest known fossils are a group of marine
  cyanobacteria.
• prokaryotic cells
• (no nucleus)
• added oxygen toatmosphere
• deposited minerals

3

• Some cyanobacterial lived in colonies and formed
  stromatolites (domed, rock structures made of
  layers of cyanobacteria and sediment).
• Fossil stromatolites provide evidence of early
  colonies of life 3.5 BYA

4

• The addition of oxygen into the atmosphere by
  photosynthesizing bacteria made it possible for
  oxygen using organisms to evolve.

5
Eukaryotic (multicellular) cells may have evolved
through endosymbiosis. (symbiosis- 2 organisms
that depend on each other for mutual benefit)

• Endosymbiosis is a relationship in which one
  organism lives within the body of another.
• Mitochondria and chloroplasts (energy production
  organs within cells) may have developed through
  endosymbiosis between early cells and bacteria.

6
The evolution of sexual reproduction led to
increased diversity.

• Early cells reproduces through asexual
  reproduction.
• Sexual reproduction may have led to the evolution
  of multicellular life.

Asexual Reproduction Sexual Reproduction
1 cell splits into two Two parents donate genes
Fast, produces many offspring Requires time and energy
Produces exact copies of parent cells Genetic variation in offspring, leading to adaptation and evolution