Dino (Paste into Notability)

Rocks and Time 1/21 (pasted)

  • James Hutton (1726 - 1797)

    • Scottish physician and naturalist, “The Father of Geology”

    • Introduced many ideas still used in geology today

  • Uniformitarianism

    • The present is the key to the past

    • Hutton’s original definition included both process and rate

    • Actualism — uniformitarianism, minus statement of rate

  • Rock Cycle

    • Transition between the three rock types — igneous, sedimentary, metamorphic

    • Rock Types: Igneous rocks form by the cooling of molten material

    • Rock Types: Extrusive/Volcanic igneous rocks cool more rapidly at the Earth’s surface

    • Rock Types: Intrusive/Plutonic igneous rocks cool more slowly under the Earth’s surface

    • Rock Types: Sedimentary grains can be made through biological means and the breakdown of pre-existing rocks by water, air, and ice

    • Rock Types: These sediments can become bonded together into solid sedimentary rocks through compression and/or cementation

    • Rock Types: When pre-existing rocks are exposed to enough heat and pressure, they are altered into metamorphic rocks

  • Sedimentary Rocks

    • Formed of three basic kinds of particles:

    • Fragments of other rocks (clasts)

    • Crystals which form through chemical reactions in water

    • Debris from organisms

  • Clastic Rocks

    • Clasts are formed by:

      • Weathering: Physical and chemical processes that break down rocks at Earth’s surface

    • And are transported by:

      • Erosion: processes that loosen rock and transport the resulting products

  • Breccias and Conglomerates

  • Sandstones

  • Siltstones and Shales

    • Preferred for preserving fossils

  • Chemically Derived Sediments

    • Form through the precipitation of inorganic material in water

    • Precipitation — formation of a solid material as a result of a chemical reaction

  • Evaporites

  • Biologically Derived Sediments

    • Material that was once part of a living organism

  • Becoming Rocks

    • Lithification / Diagenesis

      • The process by which rocks are formed

    • Lose clasts form clastic rocks by:

      • Compaction

      • Cementation

  • Compaction

    • Sediments become compressed as more and more sediments are deposited on top of them (loading)

  • Cementation

    • Crystals precipitate out of groundwater, binding loose grains together

  • Stratigraphy

    • The study of rock layers (strata) and layering (stratification)

      • Age relationships

      • Spatial relationships

      • Compositions

      • Origins

    • Rocks (especially sedimentary rocks) often form in distinct layers

  • Nicolas Steno

    • Developed three of the founding principles of stratigraphy in 1669

    • Steno’s 3 Laws

      • Superposition — In undisturbed rock layers, the oldest lie at the bottom and successively higher layers are progressively younger

      • Original horizontality — Almost all rock layers are horizontally oriented as they form

      • Later continuity — Rock layers originally form in large, unbroken, flat expanses

  • Theory of the Earth — 1795 (by James Hutton)

    • Introduced the principle of cross-cutting relationships

  • Cross-cutting relationships

    • A geological feature that cuts through another is the younger of the two features

  • Charles Lyell

    • Principles of Geology — 1830

    • Refined the principle of cross-cutting relationships

    • Introduced the principle of inclusions and components

  • Law of Included Fragments

    • Clasts within a rock are older than the rock itself

  • William Smith

    • Strata Identified by Organized Fossils — 1816

    • Introduced the principle of faunal succession

  • Faunel Succession

    • The fossils contained in successive layers of rock occur in predictable orders and combinations

  • Lithostratigraphy

    • A branch of stratigraphy which uses features of rock layers to perform geologic correlations

    • Steno’s 3 Laws, etc

    • Relative dates

  • Arriving at Absolute Dates

    • Human History is a miniscule portion of all of Earth history

    • Written histories only go back so far

  • Antoine-henri Becquerel (1852-1908)     

    • French physicist

    • Discovered radioactive decay in 1895

    • Nobel Prize in 1903 with Marie and Pierre Curie

  • Radioactive Decay

    • Isotope - Atoms of a single element which vary in the number of neutrons

    • Some isotopes are naturally unstable

    • Radiation — Particles emitted during the breakdown of these unstable isotopes

    • Radioactive elements occur naturally

      • Various elements in rocks

      • Carbon 14 in living organisms

    • Not all of them are harmful

    • The original isotope is called the parent isotope

    • After undergoing radioactive decay, the ensuing isotope is called the daughter isotope

  • John Joly (1857 - 1933)

    • Irish physicist

    • 1899 — Attempted to use ocean salinity to determine the age of the Earth

    • 1903 — Proposed that the radioactive decay of radium could be used to find the age of the Earth

  • Ernest Rutherford (1871-1937)

    • British (New Zealand) chemist and physicist

    • Discovered the concept of radioactive “half-lives”

  • Half-Life

    • Radioactive isotopes decay at a constant geometric rate

    • No matter the amount of parent isotope present in a sample, over a set amount of time, half of it will decay into its daughter

    • That set period of time is called a half-life

    • Different radioactive isotopes have different half-lives

    • Example

      • 50% parent; 50% daughter

      • 25% parent; 75% daughter

      • 12.5% parent, 87.% daughter

      • 6.25% parent, 93.75% daughter

      • 3.125% parent, 96.875% daughter

  • Geologically Useful Radioactive Isotopes

    • Rubidium 87 → Strontium 87 (48.8 billion years)

    • Potassium 40 → Argon 40 (1.3 billion years)

    • Uranium 235 → Lead 207 (0.7 billion years)

    • Uranium 238 → Lead 206 (4.6 billion years )

    • Uranium 234 → Thorium 230 (245,000 years)

    • Carbon 14 → Nitrogen 14 (5,730 years)

  • Carbon 14 Dating

    • C 12 and C 14 occur in predictable rates in all living organisms

    • C 12 is stable, C 14 is not and decays into N 14

    • Ratio of C 14 relative to C 12 can help determine how much has decayed

    • Useful for dating organic material

    • However, the half-life is fairly short — 5,730 years

    • Therefore radiocarbon dating is only useful on materials younger than 70,000 years

  • Radiometric Dating

    • So, geologists typically use different radioactive isotopes often found in igneous rocks

    • Half-lives are longer

    • Metamorphism and partial melting can reset the ‘clock’