GeoScience 106

Environment

The surrounding physical, chemical, and biological factors that influence or affect an organism.

Geology

The study of the solid Earth.

Main goal of Environmental Geology

To explore how Earth's geology and its environment influence one another.

9 Major Environmental Issues Facing Earth Today

1. Water pollution, 2. Natural hazards, 3. Drought, 4. Deforestation, 5. Ocean acidification, 6. Sea-level rise, 7. Air pollution, 8. Nuclear radiation, 9. Climate change.

Evidence for the Big Bang (4 key points)

1. Olbers' paradox (sky isn't infinitely bright), 2. Hubble's Law (distant galaxies move away faster), 3. Cosmic Microwave Background Radiation (matches blackbody spectrum), 4. Observed H/He ratio in oldest stars.

Gravity

An attractive force between all physical bodies that increases with mass and decreases with distance.

Limit of stellar fusion before a supernova

Fusion inside healthy stars only produces elements up to iron (Fe, 26 protons).

How elements heavier than iron form

During a supernova: iron fusion removes energy, causing the star to collapse and explode, creating high-pressure shock waves that fuse heavier elements and scatter them into space.

Age of Earth

4.54 ± 0.04 billion years ago (Ga).

Early Earth differentiation process

Heating from radioactive elements and meteor bombardment caused dense iron to sink to the center while less dense silicate rocks floated and gases/water vapor escaped to the surface.

What early rocks reveal about early Earth history

Intense volcanism, metamorphism, and evidence of contact with liquid water (oceans).

Importance of Earth's Moon

It is unusually large relative to Earth, stabilizing Earth's rotational axis and climate.

The "Big Whack"

The collision roughly 4.5 Ga ago that formed the Moon; evidenced by similar Earth-mantle composition, hot origin (few volatiles), and Earth's tilted axis.

Acasta Gneiss

The oldest known crust on Earth (4.02 Ga), located in the Northwest Territories, Canada.

Stromatolites

Layered sedimentary structures built by cyanobacteria; rare today due to population controls (predation, space, resources).

3 Reasons Earth is the "Goldilocks" planet for life

1. Early differentiation allowed gases/water to escape via volcanism, 2. Moon-stabilized axial tilt allows mild seasonal variation, 3. Ideal distance from the Sun permits water in solid, liquid, and vapor states.

Law of Superposition

In undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest are at the top.

Principle of Original Horizontality

Sedimentary layers are originally deposited horizontally under the action of gravity.

Principle of Cross-Cutting Relationships

If a magmatic intrusion or fault cuts through a body of rock, the intrusion/fault is younger than the rock it cuts.

Principle of Faunal Succession

Fossil species succeed one another in a definite and recognizable order; a specific creature only appears over a single time interval.

Stratigraphic Correlation

Matching rock bodies from different locations based on shared fossil content or rock characteristics.

Radiometric Dating

Determining absolute rock age by measuring the relative ratio of unstable parent isotopes to stable daughter products.

The Great Oxidation Event (Steps)

1. Cyanobacteria begin photosynthesis using atmospheric CO2, 2. Oxygen binds with dissolved iron in seawater, precipitating magnetite (Fe3O4) and hematite (Fe2O3), 3. Oxygen drops and chert forms, repeating in banded layers.

Proterozoic Eon

2.5 Ga - 539 Ma ("earlier life"); characterized by single-celled life, early multi-cellular soft-bodied organisms (jellyfish, burrows), and NO hard parts.

Phanerozoic Eon

539 Ma to present ("visible life"); begins with the evolution of shells and hard parts (Cambrian Explosion).

Paleozoic Era

539 - 252 Ma ("old life"); life moves to land (fish/amphibians, massive swamps forming coal); ends with the Permian Extinction.

End-Permian Extinction

252 Ma; the most severe extinction event in Earth history, killing >90% of marine species and >75% of terrestrial species simultaneously.

Mesozoic Era

252 - 66 Ma ("middle life"); Age of Dinosaurs, warm climate (~10°C hotter than today), first birds and small mammals appear.

Cenozoic Era

66 Ma - present ("new life"); Age of Mammals; characterized by climate fluctuation between warm periods and ice ages.

Anthropocene Epoch

Proposed geologic epoch starting ~1800 CE marked by human impact on global chemistry, erosion, and biodiversity.

Evidence for the Anthropocene

Global chemistry changes (fertilizer nitrogen, methane, CO2), physical landscape changes (dams, deforestation), and altered species distribution/extinction.

Mineral

A naturally occurring, inorganic solid with a defined chemical composition and a regular, repeating internal atomic structure.

4 Ways minerals affect the environment

1. Supply nutrients to soil/streams, 2. Neutralize acids, 3. Modulate topography, 4. Regulate climate (silicate weathering consumes CO2).

Top 2 elements in the WHOLE Earth (by weight)

Iron (32.1%) and Oxygen (30.1%).

Top 2 elements in Earth's CRUST (by weight)

Oxygen (46.6%) and Silicon (27.7%).

Silicate Tetrahedron

The fundamental building block of silicates: SiO4 (-4 charge).

Silicate mineral crystallization temperatures

Simple structures crystallize at high temperatures; complicated structures crystallize at low temperatures.

Igneous crystal size vs. cooling rate

Fast cooling/crystallization produces small crystals; slow cooling produces large crystals.

Extrusive vs. Intrusive Igneous Rocks

Extrusive (volcanic): cools quickly at Earth's surface with small crystals. Intrusive (plutonic): cools slowly underground with large crystals.

Ocean floor composition

Entirely made of basalt (extrusive mafic igneous rock).

Physical Weathering

Physical disintegration of rock into smaller particles without changing chemical composition (e.g., frost wedging, root growth, pressure release).

Chemical Weathering

Transformation of mineral chemistry by air and water (e.g., dissolution, oxidation/rusting, hydrolysis).

Lithification

The process of turning loose sediment into sedimentary rock via compaction (pressure) and cementation (precipitated minerals like calcite).

Chemical Sedimentary Rocks

Rocks formed from minerals precipitated out of solution, often aided by organisms (e.g., limestone/calcite shells, chert).

Metamorphic Rocks

Rocks formed under high heat and pressure without melting; key features include recrystallization and foliation (banding/wavy appearance).

Identify: Sheet Silicates

Low hardness (2-4), perfect planar cleavage into thin sheets (e.g., biotite, muscovite), dull/pearly luster.

Identify: Framework Silicates

High hardness (6-7), vitreous to earthy luster, often white to pink (e.g., quartz, feldspar).

Identify: Carbonate Minerals

Soft, glassy luster, fizzes under weak hydrochloric acid (HCl) (e.g., calcite, dolomite).

Identify: Sulfide Minerals

Metallic luster, often smells sulfurous/rotten eggs (e.g., pyrite, galena, sphalerite).

Identify: Iron Oxides

Black, gray, or rusty color; earthy to metallic luster; often magnetic (e.g., hematite, magnetite).

Luster: Metallic

Appearance like polished metal or chrome.

Luster: Greasy

Appearance looking like butter or fat; often feels greasy.

Luster: Silky

Parallel fibrous structure with fine fabric-like lineations.

Luster: Dull

Non-reflective, dirty appearance.

Luster: Vitreous

Glassy appearance (like glass).

Luster: Waxy

Appearance like candle wax.

Mineral Class: Carbonates

Metals combined with a CO3 group (e.g., calcite, dolomite).

Mineral Class: Oxides

Metals combined with Oxygen (O).

Mineral Class: Hydroxides

Metals combined with an OH group.

Mineral Class: Halides

Metals combined with Halogens (F, Cl, Br, or I).

Mineral Class: Sulfides

Metals combined with Sulfur (S) (e.g., pyrite, galena).

Mineral Class: Sulfates

Metals combined with an SO4 group.

Mineral Class: Native Elements

Minerals composed of a single element (e.g., gold, copper, diamond).

Pyroxene Bonding Structure

Each silicon atom bonds to 3 net oxygens [2 + (1/2) + (1/2)], giving an SiO3 ratio in single-chain silicates.

Non-Iron Oxide Minerals

High hardness (6-9), vitreous to adamantine luster; includes Spinel (MgAl2O4), Corundum (Al2O3 - ruby/sapphire), and Rutile (TiO2).