Chapter 1 - The Earth

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.

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