Earth System Science and the Rock Cycle

Earth System Science

  • Today's focus: Chapters 3 (pp. 64-76), 4 (pp. 104-105), and 7 (pp. 185-204, 209-211).
  • Recommended viewing: Men of Rock: Deep Time on YouTube.
  • Tomorrow's topic: Chapter 4, pp. 101-105.
  • Readings are in the EAOS111 Schedule.

Key Aims of Earth System Science

  • Describe the driving processes and measure the fluxes of materials and energy within and between Earth’s reservoirs.
  • Explore how the volume, direction, and efficiency of these exchanges change over time.
  • NASA Earth Observatory: http://earthobservatory.nasa.gov
  • Holistic approach to understanding the planet.

Earth System Thought Experiment

  • Energy: Kinetic energy.
    • Reservoirs: atmosphere, hydrosphere, geosphere.
  • Matter: Carbon atoms.
    • Reservoirs: geosphere, atmosphere, biosphere.
  • Questions to consider:
    • How to measure the rate and efficiency of flux?
    • How do the source and sink change as a result of the transfer?

Cycles in the Earth System

  • Constant movement of material or energy between reservoirs produces cycles.
  • Natural cycles are not simple and exist in a state of dynamic equilibrium.
  • Earth hosts hydrologic, energy, rock, tectonic, and biogeochemical cycles.
  • NASA Earth Observatory: http://earthobservatory.nasa.gov

Studying Earth System Interactions

  • Methods:
    • MODIS (Moderate Resolution Imaging Spectroradiometer).
    • IPCC AR4 (Intergovernmental Panel on Climate Change, Assessment Report 4).

Studying Earth System Interactions Over Time

  • Short timescales: time series observations (e.g., South Pole Station, Mauna Loa Observatory).
  • Long timescales: written records, oral histories.
  • Deep time: geological record.

Learning Outcomes

  • Describe how the three main rock types are formed.
  • Identify the processes that transfer material between reservoirs in the rock cycle.
  • Explain the principle of uniformitarianism and how it supports the idea of Earth’s vast history.

Looking Ahead

  • Lab and field trip skills:
    • Reading the geological record to identify past Earth system interactions.
    • Reconstructing key events in the geological history of Zealandia.

Minerals

  • Minerals are the building blocks of rocks.
  • Definition: Naturally occurring, inorganic, crystalline solid with a definable chemical composition.
    • Examples: Diamond (C), Calcite (CaCO3), Quartz (SiO2), Ice (H_2O).
    • Not a mineral: Polycrystalline silicon, Mineral water.

Classification of Rocks

  • Distinguished by: process of formation and lithologic character.
  • Types: Sedimentary, Igneous, Metamorphic.
  • The rock cycle illustrates the relationships between these rock types.

The Rock Cycle

  • Sedimentary Rock:

    • Formation: Compaction and/or Cementation of Sediments.
    • Process: Deposition and Burial.
    • Source: Weathering & Erosion of other rock types.

  • Metamorphic Rock:

    • Formation: Metamorphism (Heat and/or Pressure).
    • Source: Igneous or Sedimentary Rocks.

  • Igneous Rock:

    • Formation: Solidification of Magma.
    • Process: Melting.
    • Source: Any rock type.

Making a Sedimentary Rock

  • Mechanical & Chemical Weathering of Existing Rock Masses.
  • Transportation of Weathered Products by AIR, WATER, or ICE.
  • Sedimentary Deposition.
    • Chemical Precipitation, Settling.
    • Detrital Sediments, Chemical Sediments.
  • Lithification (Compaction, Dewatering, Cementation).
    • Detrital Sedimentary Rocks, Chemical Sedimentary Rocks.

Making an Igneous Rock

  • Magma needs to solidify.

Making a Metamorphic Rock

  • Apply pressure from deep burial (~260 atm per km of depth).
  • Apply heat from plutons or ‘normal’ geothermal gradient (~25°C/km).
  • Deform old rock from directed stresses and redistribute fluid to transform minerals.

Age of the Earth - Historical Perspectives

  • James Ussher (1581-1656), Archbishop of Armagh:
    • Calculated the Earth's age based on biblical references.
    • Determined creation occurred on “nightfall preceding Sunday, 23 October 4004 BC”.
  • John Lightfoot (1602-1675), Vice-Chancellor, Cambridge University:
    • Another biblical calculator.
    • Determined creation occurred on “nightfall near the autumnal equinox, in the year 3929 BC”.

Abraham Gottlob Werner (1749–1817)

  • “The father of German Geology”.
  • Applied the scientific method to a Biblical explanation.
  • Developed a “chronological succession”.
  • Prevailing culture required Werner to fit his observations into a framework of biblical events.
  • Basic questioning: the foundation of Earth science.

James Hutton (1726-1797)

  • Background in Medicine, Chemistry, Business, Farming, then Geology.
  • Scottish Enlightenment figure.
  • Challenged the idea that all sedimentary strata resulted from ONE catastrophic flood (Werner's suggestion).

Hutton's Questions

  • Sediment is clearly being transported to the oceans today – so what happens to it when it gets there?
  • Are new sedimentary rocks being formed today?
  • How long has this process been going on?
  • How long can mountains exist if they are being continually worn away?
  • If erosion and sediment transport have always been happening – and since sediment transport is gravity-driven and only goes downhill – why isn’t the Earth flat?
  • Is there some way of creating new mountains out of old sedimentary strata?
  • If so, are there definable relationships between older sedimentary rocks and younger strata formed by different periods of erosion, transportation and deposition? (in contrast to the flood hypothesis).

Hutton's Discovery: Geologic Time

  • “… no vestige of a beginning, no prospect of an end” - James Hutton, 1785
  • Siccar Point as Hutton's proof.
    • Observed “Old Red Sandstone” overlying “Schistus” (metamorphosed sandstone and shale).
  • “Old continents are wearing away and new continents are forming at the bottom of the sea” – the original Earth system.

Unconformity at Jedburgh

  • Hutton’s ideas didn’t become popular until his friend John Playfair published Illustrations of the Huttonian Theory of the Earth in 1802.
  • The importance of communication.

Uniformitarianism

  • "the mind seemed to grow giddy by looking so far into the abyss of time” - John Playfair, 1788
  • “The present is the key to the past” - Charles Lyell (1797-1875), Principles of Geology, 1833.

The Geologic Record

  • The memory bank of Earth’s history.
  • "a vast proportion of the present rocks are composed of materials afforded by the destruction of bodies, animal, vegetable and mineral, of more ancient formation" - John Playfair, 1788

Today's Key Ideas

  • Earth science is grounded in modern observation.
  • Geologic records are a “memory bank” of Earth processes.
  • Rock types and their relationships are important.