Geologic Time Scale

• Earth’s past eras have been separated by major events:

  • Key Principles of the geologic time scale:

    • Strata (Rock layers) are laid down in succession representing a slice of time.

    • Principle of Superposition: Any given layer is older than the layers above them and younger than the layers below them.

• Complications to the Geologic Time Scale

  • Layers are eroded, distorted, tilted, or inverted after deposition

  • Layers in different areas laid down at the same time can look different

  • A layer from one area only tells a part of Earth’s history

Earth’s Structure

• Earth can be divided into 3 sections:

  • The Biosphere

    • Includes all forms of life both on land and sea.

  • The Hydrosphere

    • Includes all forms of water.

  • The Internal Structure

    • Divided into the crust, mantle, and core.

• The Layers of the Earth

  • The Crust

    • Makes up 0.5% of Earth’s total mass.

    • Subdivided into the continental crust and the oceanic crust.

    • The crust is rocky and brittle.

  • Continental Crust

    • Extends down 20-30 miles.

    • Continental Crust is stratified (layered) and becomes more dense with depth.

    • Largely composed of sedimentary, volcanic, and granite-like rocks

    • Older areas contain metamorphic rocks.

  • Oceanic Crust

    • Relatively thin part of the crust.

    • Consists of Basaltic Rock overlain with sediments.

    • Younger and contains different chemical composition

  • Mantle

    • Most of Earth’s mass is in the mantle.

    • Composed of iron, magnesium, aluminum, and silicon-oxygen compounds.

    • Most of the mantle is solid.

    • The asthenosphere (upper third) is more plastic-like.

  • Lithosphere

    • It is broken up into huge sections called tectonic plates.

    • The movement of the lithosphere causes a lot of Earth’s events.

  • Core

    • Mostly composed of iron.

    • Outer core is molten.

    • Inner core is solid.

Plate Tectonics

• Plate Tectonic Theory

  • Earth’s lithosphere is divided into huge sections called tectonic plates that drift over the mantle

  • Arose from the concept of seafloor spreading and continental drift.

• Continental Drift Theory

  • Alfred Wegener proposed that all continents used to be one single landmass.

  • Wegener believed that the supercontinent started breaking apart 200 million years ago.

• Seafloor Spreading Theory

  • Alternating magnetic patterns were found in rocks found on the seafloor.

  • Similar patterns were found on the other sides of mid-ocean ridges and in the center of ridges.

  • Suggested that new crust was made at volcanic rifts zones.

  • Subduction Zones are where two tectonic plates meet together and one plate slides under the other and moves toward the mantle.

• Types of Boundaries - Convergent, Divergent, Transform

  • Transform Boundaries

    • Occur when plates slide past each other.

    • They frequently cause earthquakes because of friction and the stress buildup between them.

  • Divergent Boundaries

    • Occur when two plates slide apart from each other.

    • The space created between the two plates will fill up with molten magma.

    • Can create massive fault zones in the oceanic ridge system and are areas of frequent oceanic earthquakes.

  • Convergent Boundaries

    • Occurs when two plates slide together

    • Commonly forms subduction zones or an orogenic belt.

    • When a dense oceanic plate subduct a less-dense continental plate, an oceanic trench can form, and a mountain range on the continental side.

    • When two oceanic plates converge, they create an island arc - a chain of volcanic islands rising from the seafloor.

    • When two continental plates collide, mountain ranges are created because of the crust being compressed and pushed upward.

Earthquakes

• Earthquakes

  • They occur during abrupt movement on a fault, tectonic plate boundaries, or along mid-ocean ridges.

  • A massive store of energy is released in a short period of time when plates slide past each other.

• Focus: The place where all the energy is released.

• Richter Scale

  • The strength of an earthquake is measured using the Richter scale.

  • It compares the amplitudes of waves instead of the strength of the earthquakes.

• Body and Surface Waves

  • Body Waves

    • Body waves travel through Earth’s interior. There are two types - P waves and S waves.

      • P waves travel throughout Earth and are caused by the expansion and contraction of bedrock.

      • S waves are produced when a material moves either vertically or horizontally.

    • Surface waves produce rolling and/or swaying motions. They are slower than P and S waves. These waves cause damage and ground motion.

Tsunamis

• Tsunamis

  • Series of waves created when a body of water is rapidly displaced, usually from an earthquake.

  • They can be generated when plate boundaries move and displace the water vertically.

Volcanoes

• Volcanoes

  • Divided into 4 categories - active, inactive, dormant, extinct.

  • Active volcanoes produce magma at the surface.

  • Majority of active volcanoes produce magma at subduction zones or mid-ocean ridges.

  • Active volcanoes produce ejecta (lava rock/ash), molten lava, and gases such as sulfur dioxide.

• Volcanic Eruptions

  • Eruptions occur whenever pressure inside a magma chamber forces molten magma up to the top of the volcano to erupt.

  • Benefits of volcanic eruptions include producing land, and increased soil production from the erosion of lava rock.

Solar Intensity, Seasons, and Longitude/Latitude

• Solar Intensity

  • Factors that affect the amount of solar energy at the surface of the earth include Earth’s rotation, the tilt of Earth’s axis, and atmospheric conditions.

• Seasons

  • Seasons are not caused by the distance away from the sun, but from the angle of sunlight hitting Earth.

• Latitude/Longitude

  • Longitude is East/West positions on Earth. 0 degrees longitude begins in the Prime Meridian. The degrees continue 180 degrees east/west to meet at the International Date Line.

  • Latitude is North/South positions. 0 degrees is the equator. 90 degrees north is the North Pole. 90 degrees south is the South Pole.

Soil

• Soil

  • Soil is the thin layer on the top of Earth’s surface. It affects every part of the ecosystem.

  • Soil is composed of minerals of different sizes, organic materials from the remains of dead organisms and plants, and open space that can be filled with air and water.

• Soils develop due to different factors

  • Parent Material - Rock and material from where the soil derives

  • Climate - Precipitation and Temperature

  • Living Organisms - bacteria, fungi, worms, snails, insects that help decompose

  • Topography - the characteristics of where the soil is located

• Humus

  • Dark material formed when plant and animal matter decays.

  • Earthworms often help mix humus with minerals in the soil.

  • This allows air and water to go through the soil

• Soil Quality

  • Aeration - How well the soil can absorb nutrients, water, and oxygen.

  • Degree of soil compaction - How compact the soil is.

  • Nutrient - Holding Capacity - How well the soil can contain and hold nutrients

  • Permeability - The capacity that can allow water and oxygen to pass through it

  • pH - How acidic or basic a soil is.

  • Pore Size - The space between soil particles.

  • Size of soil particle - Determines the amount of water and nutrients that the soil can hold

  • Water - Holding Capacity - Controlled primarily by the soil texture.

• Soil Food Web

  • Community of organisms living their whole lives or part of their lives in the soil. Describes the complexity of the living system in the soil.

• Soil Erosion

  • The movement of weathered rock or soil components from one area to the other.

  • Caused by human activities, flowing water, wind.

  • Causes damage to the soil, agriculture, canals, and dams.

• Landslides and Mudslides

  • Occurs when masses of rock, earth, or debris moves down a slope.

  • Mudslides tend to flow in channels.

  • Landslides are caused by disturbances in the natural stability of a slope.

  • Mudslides occur when water rapidly collects in the ground and causes in a surge of water-filled rocks.

The Rock Cycle

• Igneous Rocks

  • Formed by cooling

  • Broken down by weathering and water transport.

  • Most soil comes from Igneous Rocks

• Metamorphic Rocks

  • Formed by intense heat and pressure.

  • High Quartz content forms sandy soil.

  • Slate forms silty soil.

  • Marble forms limestone clay.

• Sedimentary Rocks

  • Formed by piling and cementing various materials over time. Fossils form in sedimentary rocks.