12.4 Early Single-Celled Organisms
KEY CONCEPT
Single-celled organisms existed 3.8 billion years ago.
12.4 Early Single-Celled Organisms
Microbes have changed the physical and chemical
composition of Earth.
• The oldest known fossils are a group of marine
cyanobacteria.
– prokaryotic cells
– added oxygen to
atmosphere
– deposited minerals
12.4 Early Single-Celled Organisms
• Fossil stromatolites provide evidence of early colonies of
life.
12.4 Early Single-Celled Organisms
Eukaryotic cells may have evolved through
endosymbiosis.
• Endosymbiosis is a relationship in which one organism lives
within the body of another.
• Mitochondria and chloroplasts may have developed through
endosymbiosis.
12.4 Early Single-Celled Organisms
The evolution of sexual reproduction led to increased
diversity.
• Genetic variation is an advantage of sexual reproduction.
• Sexual reproduction may have led to the evolution of
multicellular life.