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.