5.3 The co-evolution of life and Earth's environment

Life has profoundly shaped Earth's systems over billions of years. From altering the atmosphere through photosynthesis to influencing ocean chemistry and rock formation, living organisms have been key players in our planet's evolution.

The interplay between life and Earth's environment is complex and dynamic. This relationship has led to major events like the Great Oxygenation Event and the formation of unique geological features, highlighting the interconnectedness of life and our planet.

The Influence of Life on Earth's Environment

Life's influence on Earth systems

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• Life significantly altered Earth's atmosphere, oceans, and geology throughout history
  • Atmosphere: Early life (cyanobacteria) produced oxygen through photosynthesis leading to the Great Oxygenation Event (GOE) which allowed for the evolution of more complex life forms and influenced levels of other gases (carbon dioxide, methane)
  • Oceans: Biological processes (photosynthesis, calcification) altered ocean chemistry, organisms (corals, shellfish) contributed to sedimentary rock formation, life played a role in nutrient and element cycling
  • Geology: Biological processes influenced rock formation and weathering, burial of organic carbon formed fossil fuels, life contributed to certain mineral deposits (banded iron formations)

Photosynthesis and atmospheric oxygen

• Photosynthesis converts sunlight into chemical energy releasing oxygen as a byproduct
  • Cyanobacteria first performed oxygenic photosynthesis gradually oxygenating Earth's atmosphere
  • Great Oxygenation Event (GOE) ~2.4-2.1 billion years ago marked significant increase in atmospheric oxygen
• Oxygenation of Earth's atmosphere profoundly impacted evolution of life
  • Higher oxygen levels allowed evolution of more complex life (eukaryotes, multicellular organisms)
  • Ozone layer formed from atmospheric oxygen provided UV protection enabling life to colonize land
  • Oxygen allowed evolution of aerobic respiration, a more efficient energy production form

Earth as a Self-Regulating System

Gaia hypothesis and self-regulation

• Gaia hypothesis (James Lovelock, Lynn Margulis) suggests Earth functions as a self-regulating system
  • Proposes living organisms interact with inorganic surroundings to maintain conditions favorable for life
  • Includes regulation of Earth's surface temperature, atmospheric composition, ocean salinity
• Gaia hypothesis emphasizes interconnectedness of life and Earth's environment
  • Feedback loops between life and environment help maintain relatively stable state (homeostasis)
  • Carbon cycle example: exchange of carbon between atmosphere, oceans, biosphere helps regulate Earth's temperature
• While controversial, Gaia hypothesis inspired research into complex interactions between life and Earth's environment

Co-evolution of life and environment

• Banded iron formations (BIFs) provide evidence for co-evolution of life and Earth's environment
  • BIFs are sedimentary rocks with alternating iron-rich and silica-rich bands formed during Precambrian era
  • BIF formation linked to atmospheric oxygenation by photosynthetic cyanobacteria
  • As oxygen increased, dissolved ocean iron oxidized and precipitated forming iron-rich BIF layers
• Evolution of land plants another example of co-evolution of life and Earth's environment
  • Land plants emerged ~470 million years ago during Ordovician period
  • Land plant colonization significantly impacted Earth's atmosphere, hydrosphere, lithosphere
    1. Plants increased weathering rate and soil formation altering Earth's surface
    2. Photosynthesis by land plants contributed to further atmospheric oxygenation
    3. Root and leaf evolution led to increased transpiration affecting water cycle and climate
  • Changing environment in turn influenced plant evolution leading to adaptations (vascular tissues, seeds)