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Lecture Outline

  • 25.1 Deep Time

  • 25.2 Origins of Life

  • 25.3 Evidence for Early Life

  • 25.4 Earth’s Changing System

  • 25.5 Ever-Changing Life on Earth

25.1 Deep Time

  • Geological Time Scale

    • Divided into four eons:

      • Hadean

      • Archean

      • Proterozoic

      • Phanerozoic

    • Eons subdivided into eras, further into periods.

  • Hadean Eon (4.6 billion years ago)

    • No rocks from this time exist; it lasted about 500-700 million years.

    • Earth was heavily bombarded by asteroids; conditions were extreme with molten rock.

    • A meteor impact led to the formation of the moon and molten mantle.

25.2 Origins of Life

  • Emergence of Life

    • Life likely began in the Archean eon.

    • Origin of organic molecules is uncertain.

      • Possible sources: meteorites, early Earth conditions.

  • Early Earth's Atmosphere

    • Combines carbon dioxide (CO2), nitrogen (N2), water vapor (H2O), and hydrogen gas (H2).

    • Characterized as a reducing atmosphere, leading to the formation of organic compounds.

25.3 Evidence for Early Life

  • Microfossils

    • 3.5 billion-year-old fossilized organisms resembling prokaryotes.

    • Evidence of life is sparse but consists primarily of microfossils and stromatolites.

  • Stromatolites

    • Mats of cyanobacterial organisms trapping minerals; oldest known are about 2.7 billion years old.

25.4 Earth’s Changing System

  • Geological Changes Affecting Life

    • CO2 levels in the atmosphere have fluctuated, leading to changes in temperature and conditions for life.

    • Major shifts in CO2 from ancient to present atmospheres affecting biological and geological processes.

  • Glaciation Events

    • Earth underwent significant cooling events leading to global glaciations, termed “Snowball Earth.”

25.5 Ever-Changing Life on Earth

  • Evolution of Life Forms

    • Life evolved into three main domains: Eubacteria, Archaea, and Eukaryotes.

    • Eukaryotes can be divided into five supergroups: Excavata, SAR, Archaeplastida, Amoebozoa, and Opisthokonta.

  • Evolution of Metabolism

    • Key innovations included oxygenic photosynthesis, nitrogen fixation, and the rise of multicellular organisms.

  • Endosymbiotic Theory

    • Mitochondria and chloroplasts originated from free-living bacteria through endosymbiotic events.

Key Experiments

  • Miller-Urey Experiment

    • Simulated early Earth conditions, resulting in the formation of amino acids and other organic compounds.

  • Genetic Findings

    • Horizontal gene transfer serves as a mechanism for genetic diversity in prokaryotes.

Conclusion

  • Understanding life’s evolution involves integrating geological and cellular complexity.

  • The dynamic interplay between environmental changes and biological evolution has sculpted the biodiversity we observe today.