Geology 101

Evidence for Continental Drift

Jigsaw puzzle like composition of the shorelines and continents, the appearance of the same rock sequences and mountain ranges of the same age on continents now widely separated, the matching of glacial deposits and paleoclimatic zones, and the similarities of many extinct plant and animal groups whose fossil remains are found today on widely separated continents. Glacial striations match up on continents widely separated. Main objection was that Wegener was unable to provide a mechanism capable of moving the continents. He thought that the tidal forces from the moon were strong enough to move the plates and that the continents plowed through ocean floor like icebreakers.

Jovian Planets

Jupiter, Saturn, Uranus and Neptune. All have small, rocky cores compared to their overall size and are composed mostly of hydrogen, helium, ammonia, and methane, which condense at low temperatures.

Rock

Any solid mass of mineral that occurs naturally as a part of our planet. Some are one mineral (limestone is made of calcite). Most are formed of several types of minerals (aggregates), such as granite. Some are composed of non-mineral material (obsidian, pumice, coal).

Composition and Evolutionary History of Planets

Are a consequence, in part, of their distance from the Sun.

Gases

As stated previously, volatiles escape from volcanoes. Water is most common volatile although CO2, SO2, N2 are also common. Help propel magma and rock from the volcano.

Plinian Eruption

Ash and pumice propelled by gases.

Bowen's Reaction Series

At high temperatures, olivine (ultramafic), then pyroxene (basaltic), then amphibole (mafic or andesitic), then biotite mica(andesitic), and calcium rich minerals such as plagioclase feldspar. As the magma cools further, potassium feldspar, muscovite mica and quartz are left (granitic or felsic).

Pyroclastic Flow

Avalanche of hot ash, pumice, rock fragments, and gas that rushes down the side of a volcano. Very destructive.

Mafic (Basaltic) Rocks

Basalt - Extrusive / Gabbro - Intrusive

Plate Tectonic Theory

Based on a simple model of earth. Rigid lithosphere, composed of both oceanic and continental crust, as well as the underlying upper mantle, consists of numerous variable-sized pieces called plates.

Covalent Compounds

Consist of atoms that share electrons. The most common mineral group, the silicates, contain silicon-oxygen covalent compounds.

Continental Rifting

Continental landmass is splitting into smaller segments. Pangaea broke up this way. If rifting continues, a new ocean may form, like the way the Red Sea formed.

Three Concentric Layers

Core, mantle and crust. This orderly division results from density differences between layers as a function of variations in composition, temperature and pressure.

Silicate Structures

Crsytalline structure of a silicate is reflected in the appearance of the mineral.

Obsidian

Dark, glassy rock usually formed by very rapidly cooling of silica rich lava. Usually has granitic composition even though it is dark in color. Ions in the glass are unordered.

Paleomagnetism

Direction and intensity of the Earth's magnetic field changes over time. When the rocks cool and solidify they retain some information as to what the magnetic field was like at the time.

Extrusive Eruptions

Domes

Crystal Settling

Earliest formed mineral crystals fall to bottom of magma chamber. The remaining magma now has a different chemical composition (magmatic differentiation). Many different kinds of rocks can form from one magma chamber.

Crust

Earth's outermost layer, consists of two types. Continental crust is thick (20-90 km), has an average density of 2.7 g/cm3. Contains considerable silicon and aluminum. Oceanic crust is thin, denser than continental crust, and is composed of dark igneous rocks basalt and gabbro.

Important Non-Silicate Materials

Economically important. Oxides - Hematite and Magnetite (iron ores) Sulfides - Galena (lead ore), sphalerite (zinc ore), Calcopyrite (copper ore) Carbonates - Calcite (makes up limestone and marble), Dolomite (makes up dolostone), both used in construction Halite - Rock Salt Gypsum - Used in plaster Both minerals found in thick layers left over from the evaporation of ancient seas.

Covalent Bonding

Electrons are Shared

Ionic Bonding

Electrons are transferred

Historical Geology

Examines the origin and evolution of Earth, its continents, oceans, atmosphere and life.

Pegmatitic

Exceptionally course grained that cooled very slowly (big crystals)

Physical Properties of Minerals - Crystal Form

External expression of a mineral's internal orderly arrangement of atoms. Can be tricky to use to identify minerals because many crystals grow in confined spaces and might not develop smoothly faces.

Rhyolite

Extrusive equivalent of granite, same composition with aphanitic texture.

Dark Silicates - Olivine

Family of high temperature minerals. Black to green in color with glassy luster and conchoidal fracture. Much of the earth's mantle is made of olivine, common in Hawaii.

Lava Domes

Felsic

Alphanitic Texture

Formed quickly near earth's surface

Phaneritic Texture

Formed slowly deep in the Earth

When Mafic Lava Cools

Forms columnar joints.

Geology

From Greek geo and logos. Defined as the study of Earth but now must also include the study of the planets and moons in our solar system. Nearly every aspect of geology has some economic or environmental relevance.

Pumice

Has a glassy texture like obsidian but formed when gas escapes through lava, so it looks frothy.

Theory

Has various meanings and is frequently misunderstood and misused. In scientific usage, a theory is a coherent explanation for one or more related natural phenomena supported by a large body of objective evidence. From theories, scientists derive predictive statements that can be tested by observations and/or experiments so that their validity can be assessed.

Dark Silicates - Amphibole

Hornblende is the most common member. Chemically complex. Dark green to black in color. Similar in appearance to pyroxenes, it is often found in continental crust.

Other Silicate Structures

In addition to positively charged ions, the tetrahedra may link with other tetrahedra in a variety of configurations, such as single chains, double chains, or sheet structures. Linkage between tetrahedra are oxygen ions. Ratio of silicon ions differs in each of these structures.

Dark Silicates - Biotite

Iron rich member of Mica family. Like other micas, it has a sheety cleavage. Common in continental rocks.

Shield Volcanoes

Largest. Produced in association with mafic magmas. Because the lava is less viscous, the lava flows quickly and does not accumulate on top of itself, instead spreading out quickly. Broad, slightly domed in shape. Lava first emerges as Pahoehoe flows with small amounts of pyroclastics. Often have large calderas or collapsed craters. Olympus Mons is a shield volcano and the largest in our solar system.

Mixed Eruption (Strombolian, Vulcanian)

Local ash, bombs, blocks

Silicates

Made up of the silicon-oxygen tetrahedron. Fundamental building block of all silicates. Tetrahedra becomes neutral by bonding with positively charged ions.

Assimilation and Magma Mixing

Magma body can incorporate some of the surrounding host rock (assimilation). Magma bodies with different compositions can migrate and intrude on one another (magma mixing).

Intrusive Igneous Rocks

Magma that solidifies at depth is intrusive or plutonic. Usually cools slowly, can see individualized crystallized minerals.

Pyroclastics

Material that is blown out explosively from a volcano. Mafic volcanoes tend to blow out small particles and bombs. Felsic volcanoes produce both small and large fragments. Ash, dusts, and glass particles get fused together as welded tuff. Lava blocks - large chunks of rock blown out of volcanoes. Lava bombs - small blocks of rocks ejected from volcanoes.

Terrestrial Planets

Mercury, Venus, Earth and Mars, are all small and composed of rock and metallic elements that condensed at the high temperatures of the inner nebula.

Pyroclastic

Mixture of rock fragments ejected in violent volcanic eruption, most similar to sedimentary rocks.

Physical Properties of Minerals - Hardness

Moh's scale of hardness. Diamond has highest, talc has lowest. Finger nail is 2.5, glass is 5.5

Joining Silicate Structures

Most silicate structures are not neutral. They are neutralized by inclusion of positively charged ion. Most common elements are Iron, Magnesium, Potassium, Sodium Aluminum, and Calcium.

Oceanic Ridges

Narrow, but long ridges where seafloor spreading takes place. Ridges are elevated in position because they are hot and buoyant. After 80 million years, oceanic crust is fully cooled and covered in a lot of sediment. Old oceanic lithosphere is thick.

Minerals

Naturally occurring, inorganic, crystalline solids that have definite physical and chemical properties. Composed of elements such as oxygen, silicon, and aluminum, and elements are made up of atoms, the smallest particles of matter that retain the characteristics of an element. 3,800 minerals have been identified and described, but only about a dozen make up the bulk of the rocks in Earth's crust.

Porphyritic Texture

Occurs when magma with large crystals changes environments. Large crystals are called phenocrysts. Smaller crystal matrix called groundmass.

Oceanic-Continental Convergence

Old, thick oceanic crust sinks into the mantle. Continental crust is more buoyant, results in the creation of continental volcanic arcs.

Mafic Lava Flows

Pahoehoe - Smooth streams of fluid lava. Aa - Cooler, thicker and more slowly moving than Pahoehoe. Gases escaping from the surface give it a sharp spiny texture. Pahoehoe often turns into Aa as it flows.

Plate Tectonics and Mantle Convection

Part of the same system. Subducting oceanic plates drive the downward-moving portion of convection. Oceanic ridges and mantle plumes are the upward-moving portion.

Granite

Phaneritic rock made mostly of quartz and K+Na rich Feldspars with some dark silicates. Usually the bi-product of mountain building. Resistant to weathering and abundant.

Rock Cycle

Pictorial representation of events leading to the origin, destruction, or changes and reformation of rocks as a consequence of Earth's internal and surface processes.

Mafic Lava Flows

Pillow Basalts - Form when lava cools at the base of the ocean.

Transform Fault Boundaries

Plates slide past one another. Connect convergent boundaries and divergent boundaries. Most join segments of oceanic ridges.

Light Silicates

Potassium feldspars, plagioclase feldspars, quartz, muscovite and clay minerals.

Physical Properties of Minerals - Luster

Quality and intensity of light reflected from a mineral's surface. Can have metallic luster, vitreous luster, or dull luster.

Different Rocks Form From Same Magma Chamber

Recall that different minerals freeze at different temperatures. As different minerals freeze and crystallize, the magma composition evolves.

Plate Tectonic Theory

Recognition that lithosphere is divided into rigid plates that move over the asthenosphere makes up the foundation for this theory. Holds that large segments of Earth's outer part (lithospheric plates) move relative to one another. Zones of volcanic activity, earthquakes, or both mark most plate boundaries. Along these boundaries, plates separate (diverge), collide (converge), or slide sideways past each other. Provided the framework for interpreting the composition, structure, and internal processes of Earth on a global scale. Has led to the realization that continents and ocean basins are part of the lithosphere-atmosphere-hydroshpere system that evolved together with Earth's interior. Provides basis for relating seemingly unrelated phenomena, such as the formation and occurrence of Earth's natural resources, as well as the distribution and evolution of the world's biota.

Igneous Rocks

Result when magma or lava crystallizes, or when volcanic ejecta, such as ash, accumulate and consolidate. As magma cools, minerals crystallize, and the resulting rock is characterized by a texture of interlocking mineral grains. Magma that cools slowly beneath the surface produces intrusive igneous rocks, magma that cools at the surface produces extrusive igneous rocks.

Viscosity

Silica structures link together to form long chains even before the magma has cooled and crystallized. Felsic magma is thicker and more viscous than Mafic magma.

Forces That Drive Plate Motion

Slab pull - Slabs sink into the asthenosphere because they are dense and heavy. Most important force. Ridge Push - Gravity driven force resulting from elevated position of oceanic ridge. Slabs of young lithosphere slide downwards along the slippery asthenosphere. Slab Suction - As the slab descends, it sucks nearby mantle and the overriding plate down with it. This is how the basin and range province in the US southwest formed.

Cinder Cones

Smaller volcanoes that are made up entirely of pyroclastic materials.

Continent-Contitent Covergence

Sometimes an entire oceanic plate will be sub ducted, and continental landmasses collide. This collision creates large plateaus and high mountain chains.

Divergent Plate Boundaries

Spreading ridges. Occur where plates are separating and new oceanic lithosphere is forming. Places where the crust is extended, thinned, and fractured as magma, derived from the partial melting of the mantle, rises to the surface. Most commonly occur alongside the crests of oceanic ridges, for example, the Mid-Atlantic ridge. Characterized by rugged topography

Expansion of Universe

Stars and galaxies began to form and the chemical makeup of the universe changed. Initially, universe was 100% hydrogen and helium, whereas today it is 98% hydrogen and helium and 2% all other elements by weight.

Physical Geology

Study of Earth materials, such as minerals and rocks, as well as processes operating within Earth and on its surface.

Asthenosphere

Surrounds lower mantle. Has the same composition as the lower mantle but behaves plastically and flows slowly. Partial melting within the asthenosphere generates magma, some of which rises to the surface because it is less dense than the rock from which it is derived.

Mantle

Surrounds the core and accounts for 83% of Earth's volume. It is less dense than the core and is thought to be composed mostly of peridotite, a dark, dense igneous rock containing abundant iron and magnesium. The mantle can be divided into three distinct zones based on physical characteristics. Lower mantle is solid and forms most of the volume of Earth's interior.

Hypothesis

Tentative explanation. Formulated to explain observed phenomena. Then hypothesis is tested to see whether what was predicted actually occurs in a given situation. Finally, if one of the hypotheses is found, after repeated tests, to explain the phenomena, then the hypothesis is proposed as theory.

Scientific Method

The process by which theories are formulated. Orderly, logical approach that involves gathering and analyzing facts or data about the problem under consideration.

How Did Universe Composition Change?

Throughout their life cycle, stars undergo many nuclear reactions in which lighter elements are converted into heavier elements by nuclear fusion. When a star dies, often explosively, heavier elements that were formed in its core are returned to interstellar space and are available for inclusion in new stars.

Convergent Plate Boundaries

Two plates collide and the leading edge of one plate is subducted beneath the margin of the other plate and eventually incorporated into the asthenosphere. There are three different kinds 1. Subduction Zones: Oceanic-Continental 2. Subduction Zones: Oceanic-Oceanic 3. Continental Collision

Lithosphere

Upper mantle and the overlying crust constitute lithosphere, surrounds asthenosphere. Broken into plates that move over the asthenosphere, partially as a result of underlying convection cells. Interactions of these plates are responsible for such phenomena as earthquakes and volcanic eruptions and for the formation of mountain ranges and ocean basins.

Viscosity and Dissolved Gases

Volatiles in the magma make magma more fluid, but escaping gases could produce a lot of force that could create a violent eruption.

Extrusive Igneous Rocks

Volcanic. Lava - magma that flows onto the surface. Lava cools relatively quickly, usually can not see crystallized materials (too small).

Glassy Texture

When molten lava is ejected into atmosphere, like obsidian.

Ocean-Ocean Convergence

When two oceanic plates converge, the heavier, older one sinks. Over time, a volcanic island arc is formed. Island arcs evolve over time.

Physical Properties of Minerals - Color

While it is obvious what the color of a mineral is, it is unreliable diagnostic feature. Minerals can have a lot of impurities which change the overall color of the mineral.

Sun

While planets were accreting, material that had been pulled into the center of the nebula also condensed, collapsed and was heated to several million degrees by gravitational compression, resulting in the Sun.

Metallic

Another bond

Van der Waals

Another bond (mica)

Physical Properties of Minerals - Fracture

Conchoidal, such as in obsidian.

Ionic Compounds

Consist of an orderly arrangement of oppositely charged ions assembled in a definite ratio so that the compound is electrically neutral

Dark Silicates - Pyroxene

Another common component of Earth's mantle. Augite is most common - dominant mineral is basalt, the igneous rock that makes up the oceanic crust.

Four Basic Forces

1. Gravity 2. Electromagnetic Force 3. Strong nuclear force 4. Weak nuclear force These powers separated and the universe experienced enormous expansion.

Big Bang

14 Billion years ago. Model for the evolution of the universe in which a dense, hot state, was followed by expansion, cooling and a less dense state. The universe has no edge and therefore no center. When the universe began, all matter and energy were compressed into an infinitely small high-temperature and high-density state in which time and space were set at zero. There is no before Big Bang. Two fundamental phenomena suggest the Big Bang occurred 1. Universe is expanding 2. It is permeated by background radiation.

Earth

4.6 billion years ago, various planetesimals in our solar system gathered enough material together to form Earth and the other planets. Early Earth was probably cool, of generally uniform composition and density throughout, and composed mostly of silicates (compounds consisting of oxygen and silicon). When meteorite impacts, gravitational compression, and heat from radioactive decay increased the temperature of Earth enough to melt iron and nickel, and homogenous composition disappeared. Replaced by concentric layers of differing composition and density, resulting in differentiated planet.

Rock

Aggregate of minerals

Continental Drift

Alfred Wegener, German meteorologist, credited with developing in The Origin of the Continents and Oceans. Proposed all landmasses were originally united in a single supercontinent called Pangaea.

Andesitic (Intermediate) Rocks

Andesite - Extrusive, Diorite - Intrusive

Solar Nebula Theory

Best explains the features of the solar system and provides a logical explanation for its evolutionary history. According to the theory, the condensation and subsequent collapse of interstellar material in a spiral arm of the Milky Way resulted in a counter-clockwise-rotating disk of gases and small grains. About 90% of the material was concentrated in the central part of the disk, thus forming an embryonic Sun, around which swirled a rotating cloud of material called a solar nebula. Within the nebula were localized eddies in which gases and solid particles condensed. During condensation, gaseous, liquid, and solid particles began to accrete over ever-larger masses called planetesimals, which collided and grew in size and mass until they eventually became planets.

Felsic and Intermediate Lavas

Block lavas - similar to Aa but smoother.

Core

Calculated density of 10-13 grams per cubic centimeter. Occupies 16% of Earth's total volume. Seismic data indicate the core consists of a small, solid inner region and a larger, apparently liquid, outer portion. Both are thought to consist mostly of iron and a small amount of nickel.

Physical Properties of Minerals - Cleavage

Can be 1 direction, which is flat sheets, 2 at 90 degrees (feldspar), 2 not at 90 degrees (hornblende), cubic (halite), rhombohedron (calcite), or octahedron (fluorite). Cleavage is when a mineral breaks into pieces that have the same geometry as each other.

Organic Evolution

Central thesis is that all present-day organisms are related and that they have descended with modifications from organisms that lived in the past. Provides conceptual framework for understanding the history of life.

Physical Properties of Minerals - Streak

Color (or lack thereof) of a mineral's streak on a streak plate.

System

Combination of related parts that interact in an organized manner. The Earth is a system of interconnected components. Principal subsystems of Earth are atmosphere, biosphere, hydrosphere, lithosphere, mantle and core.

Effusive Eruptions

Common in Hawaii, lots of lava