Notes on Earth’s Physical Systems for ENV100

Housekeeping

  • Class: ENV100 The Environment
  • Instructor: Damian Maddalena
  • Term: Fall 2024

Presentation Outline

  1. Housekeeping
    • Announcements
  2. Planet Earth
    • Formation of our Solar System
    • Evolution of the Atmosphere, Hydrosphere, and Lithosphere
    • Influence of Life on Earth’s Environmental Systems
  3. Geologic Cycles
    • Three Cycles:
      • Rock Cycle
      • Plate Tectonics Model
      • Tectonic Environments and Plate Boundaries

Announcements

  • Join the Microsoft Team for the course; details in the syllabus.
  • Weekly Outline available to keep up-to-date.
  • TA information posted on Quercus; contact TA first for inquiries.
  • Assignment 1 is now posted; due date pushed back to October 6, 23:59.

Planet Earth

Formation of Our Solar System

  • Deep Time:
    • Solar System formed ~4.6 billion years ago via gravitational collapse of a giant interstellar molecular cloud (Nebular Hypothesis).
    • How do we know?
    • Age estimated from models of stellar evolution and dating primitive solar system objects (e.g., carbonaceous chondrites).
    • Earth’s oldest rocks found in Canadian Shield (~4.3 billion years).

The Nebular Hypothesis

  1. Formation of the Solar Nebula
  2. Gravitational Collapse
  3. Formation of the Sun
  4. Formation of the Planets
  5. Planetary Differentiation
Components of the Nebular Hypothesis
  • Formation of a solar nebula from an interstellar cloud of gases (mostly H and He) and dust.
  • Gravitational collapse triggered possibly by a nearby supernova.
  • Formation of the Sun as the center of the collapsing cloud becomes denser and hotter; nuclear fusion begins.
  • Surrounding material forms protoplanets through collisions and accretion.
  • Differentiation leads to layers (core, mantle, crust) in differentiated planets like Earth.

Composition of Our Solar System

  • Jovian (outer) Planets:
    • Large, gaseous, and icy.
  • Terrestrial (inner) Planets:
    • Small, rocky, and metallic.

Evolution of the Atmosphere, Hydrosphere, and Lithosphere

Early Earth Conditions

  • Initially hostile with a first atmosphere composed mostly of hydrogen and helium; no free oxygen.
  • Active volcanism and bombardment by meteoritic debris; intense UV radiation.
  • Liquid water began to accumulate around 4.4 billion years ago due to cooling.

Water Properties Supporting Life

  • Chemical Characteristics:
      -
    1. Polar nature allows bonding with other chemicals.
    2. Liquid over a wide range of temperatures.
    3. Strong cohesion aiding chemical transport.
    4. High heat capacity, stabilizing temperature changes.
    5. Low density of ice leads to floating, insulating water.

Chemical Interactions in Early Earth

  • Atmospheric gases reacted with water, leading to mineral weathering and cyclical interactions.
  • Life's existence depended on evolving conditions of the atmosphere, hydrosphere, and lithosphere.

The Influence of Life on Earth’s Environmental Systems

Origin of Life Hypotheses

  1. Heterotrophic Hypothesis:
    • Life originated from inorganic chemicals in oceans.
  2. Panspermia Hypothesis:
    • Suggests microbes delivered from space.
  3. Chemoautotrophic Hypothesis:
    • Life began at deep-sea hydrothermal vents with chemoautotrophs.

Fossil Record as Earth’s History

  • Fossils provide information regarding past life forms, with single-celled organisms appearing ~4 billion years ago.
  • Major diversification occurred during the Cambrian Explosion.
  • The record indicates multiple mass extinctions and the extinction of the majority of species.

Biogeochemical Cycling

  • Early life forms influenced Earth's atmosphere by:
    • Building up oxygen through photosynthesis, recorded in seafloor sediment.
    • Reducing atmospheric CO2, contributing to the carbon cycle.

Geologic Cycles

Overview of Geologic Cycles

  • Types of Geologic Cycles:
    • Rock Cycle: Involves heating, melting, cooling, weathering, and reassembling of rocks and minerals.
    • Tectonic Cycle: Related to movement of lithospheric plates.
    • Hydrological Cycle: Also a geological cycle influencing many environmental factors.

Rock Cycle Detail

  • Includes three families of rock:
    1. Igneous: Formed from magma cooling.
    2. Sedimentary: Formed from sediment compaction and cementation.
    3. Metamorphic: Formed through heat and pressure.
    • Fossils indicate sedimentary rocks.

Plate Tectonics Model

  • Explains the dynamics of Earth's lithosphere via convection in the mantle, leading to movement of tectonic plates.
  • Interactions at plate boundaries include:
    • Divergent: Plates move apart; new crust created.
    • Convergent: Plates move towards each other; crust consumed.
    • Transform: Plates slide past one another; no crust created or destroyed.

Earth's Structure

  • Comprised of lithosphere (crust + upper mantle) and asthenosphere (a ductile layer allowing movement).
  • Plate movements are driven by processes like mantle convection, slab pull, and ridge push.