Earth's history is marked by major events that shaped our planet. From mass extinctions wiping out vast numbers of species to the oxygenation of the atmosphere enabling complex life, these events transformed Earth's surface and inhabitants.

Climate change, supercontinent formation, and breakup have also played crucial roles. By studying these events, we gain insights into Earth's past and potential future, understanding the delicate balance of life and the planet's systems.

Mass Extinction Events and Causes

The Big Five Mass Extinctions

• The Ordovician-Silurian extinction (440 million years ago)
  • Likely caused by global cooling and a decrease in sea level
  • Resulted in the loss of approximately 85% of marine species
• The Late Devonian extinction (375 million years ago)
  • Potentially caused by global cooling, ocean anoxia, and the Kellwasser Event
  • Led to the loss of about 75% of species
• The Permian-Triassic extinction (252 million years ago), also known as "The Great Dying"
  • The largest known mass extinction, with an estimated 96% of marine species and 70% of terrestrial vertebrate species becoming extinct
  • Possible causes include the Siberian Traps volcanism, ocean acidification, and a decrease in oxygen levels
• The Triassic-Jurassic extinction (201 million years ago)
  • Likely caused by climate change and ocean acidification resulting from the Central Atlantic Magmatic Province volcanism
  • Led to the loss of about 80% of species
• The Cretaceous-Paleogene extinction (66 million years ago)
  • Caused by the Chicxulub asteroid impact and Deccan Traps volcanism
  • Resulted in the extinction of approximately 76% of species, including non-avian dinosaurs (Tyrannosaurus rex, Triceratops)

Potential Causes of Mass Extinctions

• Global cooling and decreased sea levels (Ordovician-Silurian extinction)
• Ocean anoxia and the Kellwasser Event (Late Devonian extinction)
• Siberian Traps volcanism, ocean acidification, and decreased oxygen levels (Permian-Triassic extinction)
• Climate change and ocean acidification from the Central Atlantic Magmatic Province volcanism (Triassic-Jurassic extinction)
• Asteroid impacts (Chicxulub crater) and volcanism (Deccan Traps) (Cretaceous-Paleogene extinction)

Oxygenation of Earth's Atmosphere

The Great Oxygenation Event (GOE)

• Occurred around 2.4 to 2.1 billion years ago
• Cyanobacteria began producing oxygen through photosynthesis
  • Led to a significant increase in atmospheric oxygen levels
• Enabled the formation of the ozone layer
  • Provided protection from harmful ultraviolet radiation
  • Allowed life to colonize land
• Facilitated the evolution of aerobic respiration
  • More efficient than anaerobic respiration
  • Allowed for the development of more complex life forms (multicellular organisms)
• Caused a mass extinction of anaerobic organisms that could not tolerate oxygen
  • Provided opportunities for the diversification of aerobic life

The Neoproterozoic Oxygenation Event (NOE)

• Occurred around 800 to 540 million years ago
• Further increased atmospheric oxygen levels
• Paved the way for the Cambrian Explosion (rapid diversification of animal phyla)
• Enabled the evolution of more complex animals (arthropods, chordates)

Evidence for Climate Change

Paleoclimatic Proxies

• Ice cores, tree rings, and marine sediments provide evidence for past climate changes
  • Preserve indicators of temperature, precipitation, and atmospheric composition
• Oxygen isotope ratios in ice cores indicate global temperature changes
• Tree rings reveal annual variations in temperature and precipitation
• Marine sediments contain fossils (foraminifera) and geochemical indicators (carbon isotopes) of past climate conditions

Major Climate Events in Earth's History

• The Huronian Glaciation (2.4 to 2.1 billion years ago)
  • One of the earliest known ice ages
  • May have been caused by the decreased greenhouse effect resulting from the GOE
• The Cryogenian Period (720 to 635 million years ago)
  • Characterized by two major glaciations: the Sturtian and Marinoan
  • May have covered the entire Earth in ice (the "Snowball Earth" hypothesis)
• The Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago)
  • A period of rapid global warming caused by the release of carbon dioxide into the atmosphere
  • Led to ocean acidification and changes in marine and terrestrial ecosystems
• The Pleistocene Glaciation (2.6 million to 11,700 years ago)
  • Characterized by repeated glacial-interglacial cycles
  • Ice sheets advanced and retreated in response to changes in Earth's orbit and atmospheric greenhouse gas concentrations

Consequences of Climate Change

• Significant impacts on the distribution and evolution of life
• Species adapt to new conditions, migrate to suitable habitats, or become extinct
• Changes in ecosystem structure and function (shifts in species composition, alterations in food webs)
• Influences on human societies (agricultural productivity, water availability, sea-level rise)

Supercontinent Formation and Breakup

Supercontinent Cycle and Wilson Cycle

• Supercontinents are large landmasses formed by the convergence of multiple continents through plate tectonic processes
  • Particularly continental collisions
• The supercontinent cycle is driven by the Wilson Cycle
  • Describes the opening and closing of ocean basins due to plate tectonics
• Formation of supercontinents can lead to increased continental weathering and erosion
  • Lowers atmospheric carbon dioxide levels
  • Potentially triggers global cooling and glaciations
• Breakup of supercontinents can result in increased volcanic activity
  • Releases greenhouse gases and causes global warming

Influence on Earth's Systems

• Supercontinents influence ocean circulation patterns
  • Their configuration can alter the distribution of heat and nutrients
  • Affects marine productivity and biodiversity
• Formation and breakup of supercontinents impact global climate
  • Weathering and erosion rates change atmospheric composition
  • Volcanic activity releases greenhouse gases
• Supercontinent cycle affects the evolution and distribution of life
  • Provides opportunities for species to migrate and diversify
  • Can lead to vicariance and allopatric speciation

Examples of Supercontinents

• Nuna (Columbia)
  • Formed around 1.8 billion years ago
  • Broke up about 1.3 billion years ago
• Rodinia
  • Formed around 1.1 billion years ago
  • Broke up about 750 million years ago
• Pangaea
  • Formed around 335 million years ago
  • Began to break up about 175 million years ago
  • Consisted of two major landmasses: Laurasia (modern North America and Eurasia) and Gondwana (modern South America, Africa, Australia, Antarctica, and India)