Earth Science

Science

the study of natural phenomena

Self-correcting process:

-Scientific method

-Peer review

Steps of the scientific method:

-Observation

-Hypothesis

-Test hypothesis

-Results

-Inconsistent with hypothesis

-Revise hypothesis

-Test hypothesis (again)

Peer review

other scientists in the field critique work and/or attempt to reproduce results

The hierarchy of science

: all repeatedly test, never rejected

Theory:

set of very well-tested hypotheses explaining how changes occur

Energy from the sun, deices processes in the:

-Atmosphere

-Hydrosphere

-Biosphere

Complex planet, many interacting parts:

-Solid earth: rock

-Atmosphere: air

-Hydrosphere: water

-Biosphere: life

Why do crops grow here?

-Climate, humid, lots of rain and snow, but not too cold or hot!

Why do crops grow so well here?

-Soils!

Earthquake

a release of energy when rocks stuck and straining against each other finally break or slip by each other along a fault

Alfred Wegener

-First proposed continental drift hypothesis in 1915

-Published the origin of continents and oceans

Pangea

-Jigsaw puzzle pieces, the continents appear to ft back together if you remove the oceans

Fossils

Fossils of animals and plants that would not have been able to cross vast oceans can be found on different continents

-They would not have been able to move between continents unless the continents had been connected at one time

Paleoclimate

Paleoclimate presented in rocks and the location of glaciations

Tillites:

rocks formed from big piles of unsorted rocks and dirt

Marie Tharp

-Marie Tharp mapped the entire north Atlantic and noted the continuous notched ridge running north-south, suggesting it was a rift

Mid oceanic rift

A zone where the earth is pushing itself apart

Modern mapping of the ocean floor reveals…

-Mid-ocean ridges

-Deep trenches

-Fracture zones

Seafloor spreading

-1960, Harry Hess published his “Essay in Geopoetry.”

-He called his theory “sea floor spreading

-Upwelling mantle erupts at the mid ocean ridges

-New crust moves away from ridges, gathering sediment

-At trenches, the sea-floor dives back into the mantle

-Provided a potential mechanism for continental drift

“Geopoetry” eventually leads

Plate tectonics

The theory of plate tectonics

-Rigid lithosphere overlies weak asthenosphere

-The lithosphere is earths strong, outer layer

-The asthenosphere is a hotter, weaker region of the mantle under the lithosphere

Types of plate boundaries:

-Divergent plate boundaries

-Convergent plate boundaries

-Transform plate boundaries

Divergent plate boundaries

New ocean floor is generated as tow plates move apart

-Most divergent plate boundaries are located along the crests of oceanic ridges

Continental rifting

-Occurs when a divergent plate boundary occurs within a continent

-A landmass will split into two or more smaller segments

-Continental lithosphere can break apart

-Lithosphere stretches and thins

-Brittle upper-crust faults

-Ductile lower crust flows

-Asthenosphere melts

-Melt erupts

-Continuation of this process leads to full seafloor spreading

-Creates passive continent-ocean margins (less hazardous)

Convergent plate boundary

-Trenches

-Shallow to deep EQs

-Volcanoes on overriding plate

-Thrust faults on overriding plate

-One oceanic plate is consumed

-Overriding plate can be continental or oceanic crust

Convergent plate margins

-Two plates move toward each other at these destructive plate margins, where the older portions of oceanic plates are returned to the mantle

-Thel leading edge of one plate is bent downward, as it slides beneath the other at subduction zones

-Deep ocean trenches are the surface manifestations produced at subduction zones

Continential-Continential convergent margins

-Continued subduction can bring two continents together

Ocean-Continent

-Denser crust always subducts

Ocean-Ocean

Older, colder(denser) subducts

Transform boundaries

-Plates slide past one another and no lithosphere is created or destroyed

-Most join tow segments of an oceanic ridge system along breaks in the oceanic crust known as fracture zones

-Transform faults can also move ridge crests toward subduction zones

-A few transform faults cut through continental crusts

-Shallow earthquakes

Age of the deepest sediments

the oldest sediments are furthest from the spreading center

The thickness of ocean floor sediments verifies seafloor spreading

sediments are almost absent on the ridge crest and thickest furthest from the spreading center

Paleomagnetism

-Basaltic rocks contain magnetite, and iron rick material affected by earth’s magnetic field

-When the basalt cools below the curie point, the magnetite aligns toward the position of the north pole

-The magnetite is then “frozen” in position and indicates the position of the north pole at the time of rock solidification. This is referred to as paleomagnetism

Forces that drive plate motion:

The subduction of cold oceanic lithosphere is a slab pull force

-Elevated lithosphere on an oceanic ridge will slide down due to gravity, called the ridge force or ridge push force

-Convection

The big bang

-The big bang proposes that all matter and energy in the universe started out as a single infinitesimally small point

-It exploded and has been expanding ever since

A star is born

-Expansion and cooling allows atoms and matter to form

-Atoms bond forming hydrogen molecules

-Gravity pulls matter together, which in turn heats the collected matter

-Compacted masses form. With dense centers

-Centers continue to heat and start to emit light

-Past 10 million degrees, hydrogen begins to fuse forming helium

Stellar nucleosynthesis

-Big bang protostars formed the lightest elements

-Stellar nucleosynthesis formed elements up to Fe

-Elements with atomic numbers larger than 26 formed during star collapse

Super nova: star collapse

-Rapidly expanding shell of gas ejected into space from a star explosion whose light reached the earth in 1054. This shell is called the crab nebula

Zircons

-Originally formed by crystallization from a magma or in metamorphic rocks

-Zircons are super durable and resistant to chemical attack

-May survive, multiple geologic events, which can be recorded in rings of additional zircon, like tree rings

The hadean eon

-Volcanic outgassing created a deadly atmosphere

-Early crust was comparted by meteorites

-Forming liquid water required cooling of the surface

-Rained for 1000s of years over large surface of earth

-First evidence of oceans from marine sediments, 3.85 Ga.

-Oxygen isotope evidence of water, 4.3-4.4 Ga

Life first developed in the oceans due to:

1. Nutrients and chemicals necessary for life are found in abundance

2. Currents mix this material easily

3. Water provides protection from ultraviolet radiation

Definition of a mineral:

-Naturally occurring

-Generally inorganic

-Solid substance

-Orderly crystalline structure

-Definite chemical composition

Definition of a rock:

-A solid mass of minerals or mineral-like matter that occurs naturally

-Coal is made from the remains of compressed plants

-Lots of organic material

Minerals form when:

1.       Elements and compounds are precipitated from solution

2.       Crystallization of molten rock

3.       Deposition as a result of biological process

Cation:

Positively (+) charged ion

Anion:

Negatively (-) charged ion

Ionic bond:

exchanging electrons) attraction between cations and anions

Covalent bond

(sharing electrons) adjacent atoms share an electron

Metallic bond:

(sharing electrons) atoms are closely packed and the electrons move freely

How do we identify minerals?

Several properties are used:

-Color

-Streak

-Luster

-Hardness

-Crystal habit

-Cleavage

Color

-Not always the best indicator, many minerals can come in a variety of colors

-Certain minerals can be easily identified by color, however

Streak color

-Refers to the color of the mineral when powdered

-To determine the streak color, you will drag the mineral along wither a black or white streak plate

-Minerals have specific streak colors they will produce that can help you identify the which mineral you are looking at

Luster

Appearance of a mineral in reflected light

Mohs scale of hardness

-Resistance of a mineral to abrasion or scratching

-All minerals are compared to a standard scale called the Mohs scale of hardness

Cleavage

-Tendency to break along planes of weak bonding

-Produces smooth, flat surfaces

Cleavage is described by:

-Number of planes

-Angles between adjacent planes

-Resulting geometric shapes

-Not the same as fracture, all minerals can fracture but not all minerals have cleavage

Mineral properties

-Orderly internal atomic structures of a mineral dictates its crystal form (habit): set of faces that have a definite geometric relationship to one another (a minerals external geometry)

Basal cleavage

-One directional

-Two directional

-Three directional

Fracture

-All minerals fracture, not all will cleave

Effervescence (aka bubbling)

-Some materials with co3 (carbonate) will fizz when they interact with HCL

The silicates

-Silica and oxygen combine to form the basic building block for the silicates

The non silicates

-The remaining mineral groups are often referred to as the nonsilicates

Common light silicate minerals include:

-Feldspars

-Quartz

-Muscovite

-Clay minerals

-Igneous rocks are crystalized from:

-Magma (within the crust

-Or lava (at earth’s surface)

-Igneous ricks exposed at earth’s surface undergo weathering

-Loose material is called sediment

-Deposited sediment undergoes lithification

-Deformed by great heat and pressure if deeply buried or incorporated into a mountain chain

-Eventually enough heat will melt the rock and generate magma

-Sedimentary landscapes are the result of the erosional power of water (and wind rarely)

-Currently still happening

-Not all rocks go through the same cycle

Igneous rocks

Igneous rocks form when magma or lava cools and crystalizes

Extrusive igneous rocks:

-Volcanic

-Cool quickly at the surface

-No time for crystal formation

Intrusive igneous rocks:

-Cool within the Earth

-Long cooling time allows for large crystal growth (visible with the naked eye)

-Only exposed by uplift or erosion

Sedimentary rocks

-Sedimentary rocks start with weathering. Weathering is the transformation of a rock to reach equilibrium with its environment

Two basic categories of weathering

-Mechanical weathering

-Chemical weathering

Metamorphic rocks

-Metamorphic rocks come from the solid-state alteration of a protolith

-In easier to understand terms, you take a rock and put it under conditions in which the rock is changed without melting it

-We discuss metamorphic rocks by talking about their metamorphic grade

-Low-grade (slight changes) to high grade (substantial changes)

-And if they are foliated

-Not all metamorphic rocks are foliated

Sedimentary rocks form at or near the earth’s surface in one of several ways:

-The cementation of loose fragments of pre-existing rock

-Cementing together loose shells and shell fragments

-Accumulation of organic matter from living organisms

-Precipitation of minerals dissolved in water

Formation of sedimentary rocks

-Sedimentary rocks form in layers like the slow stacking of one sheet of paper on top of another

-The layers record a history of ancient environments

-The layers only form at the surface

-Sedimentary rocks form caps over “basement rock”

-Basement rock is generally igneous or metamorphic

Clastic rocks

: loose rock fragments cemented together

Biochemical rocks:

cemented shells of living organisms

Organic rocks:

: carbon rich remain of once living plants and animals

Chemical:

minerals that crystalize directly from water

Clastic sedimentary rocks are created by:

-Weathering

-Erosion

-Transport

-Deposition

-Lithification

Compaction:

burial adds pressure to sediment

Cementation:

: minerals grow in pore spaces

Angularity

the degree of edge or corner smoothness

Sphericity:

degree to which a clast nears a sphere

Sorting:

how similar are the grains in size?

Well sorted

all clasts have nearly the same grain size

Poorly sorted

clast sizes vary widely

Clastic rock types:

-Breccia

-Conglomerate

-Arkose

-Sandstone

-Mudstone

-Shale

Coarse clastic

gravel sized fragments indicating high energy

Breccia:

angular rock fragments

Arkose

sand and gravel with abundant feldspar

Sand clasts:

moderate energy

Sandstone:

rock comprising sand sized particles

Fine clastic

very small grains (often not visible) deposited in quiet water

Siltstones:

lithified silt deposits

Mudstones:

lithified mixture of fine sand, silt, and clay

Limestone:

sedimentary rocks made of calcium carbonate

Chalk:

made up of CaCO3 plankton shells

Micrite:

: fine carbonate mud

Chert

rock made od cryptocrystalline quartz (can’t see crystals)

Organic sedimentary rocks

-Rocks made up of organic carbon from the soft tissues of once living organisms

Coal:

altered remains (pressure and temperature) of fossil vegetation