Life in the Archaean Eon

The Archaean Eon

• The Archaean eon was a period when diverse microbial life flourished in primordial oceans.
• The oldest known fossils of living cells date back to around 3.5 billion years ago, but scientists believe cells emerged earlier.
• The first cells were prokaryotic, as indicated by the morphology of their fossilized remains.

Characteristics of Life in the Archaean Eon

• During the Archaean eon, all life-forms were prokaryotic and lasted for over 1 billion years.
• The Earth's atmosphere had very little free oxygen, so single-celled microorganisms likely used anaerobic respiration.

Prokaryotic Cells

• Organisms with prokaryotic cells are divided into two groups: bacteria and archaea.
• Bacteria are more prevalent on modern Earth, but many archaea species have been identified.
• Archaea are found in various environments, including extreme environments like hot springs.

Relationships Between Bacteria and Archaea

• Bacteria and archaea share fundamental similarities, indicating a common ancestor.
• Despite their similarities, they have distinct differences in cellular and molecular features, suggesting an early divergence in the history of life.

Energy and the Emergence of New Species

• Energy availability was a crucial factor in the emergence of new species
• Organisms require energy to survive and reproduce, and they follow two strategies to obtain energy: heterotrophy and autotrophy

Heterotrophy

• Heterotrophs derive their energy from the chemical bonds within the organic molecules they consume
• Most common sources of organic molecules are other organisms, so heterotrophs typically consume other organisms or materials from other organisms

Autotrophy

• Autotrophs directly harness energy from either light or inorganic molecules
• Plants are an important example of autotrophs, using light energy to synthesize organic molecules like glucose through photosynthesis
• Autotrophs produce food, which heterotrophs ultimately rely on

Origins of Life

• The origin of the first forms of life is unresolved, with two possible scenarios:
  • Autotrophs, such as those near deep-sea vents, may have arisen first, using chemicals as an energy source to make organic molecules
  • Heterotrophs, using the organic molecules in the prebiotic soup as a source of energy, may have been the first living cells

Explore the early life forms on Earth during the Archaean eon, including prokaryotic cells and microbial life in primordial oceans.