Understanding Earth’s Dynamic Processes: Layers, Heat, and Plate Tectonics
Understanding Earth’s Dynamic Processes
Introduction to Earth Science
- When earthquakes occur, they produce seismic waves.
- The three main layers of Earth are the crust, the mantle, and the core. These layers vary greatly in size, composition, temperature, and pressure.
Pressure: Is a force pressing on an area.
Earth’s Layers
The Crust
- Your journey to the center of Earth begins in the crust. The crust is the layer of rock that forms Earth’s outer skin. It is a layer of solid rock that includes both dry land and the ocean floor.
- The crust beneath the ocean is called oceanic crust. Oceanic crust consists mostly of rocks such as basalt.
Basalt: Is a dark rock with a fine texture.
Granite: Is a rock that usually has a light color and a coarse texture.
The Mantle
- The mantle is a layer of hot, solid rock.
- Earth’s mantle is made up of rock that is very hot, but solid. Scientists divide the mantle into layers based on their physical characteristics. Overall, the mantle is nearly 3,000 kilometers thick.
- The Lithosphere: The uppermost part of the mantle and the crust together form a rigid layer called the lithosphere.
- The Asthenosphere: Below the lithosphere, your vehicle encounters material that is hotter and under increasing pressure. This soft layer is called the asthenosphere.
The Core
- Outer Core: Is a layer of molten metal that surrounds the inner core.
- Inner Core: Is a dense ball of solid metal.
Heat Transfer Mechanisms
- Radiation: The transfer of energy through space.
- Conduction: Heat transfer within a material or between materials that are touching.
- Convection: Heat transfer by the movement of currents within a fluid.
Density: Is a measure of how much mass there is in a volume of a substance.
Convection Currents
- Convection Currents: Is the flow that transfers heat within a fluid. Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.
Convection Currents in Earth
- Heat from the core and the mantle itself causes convection currents in the mantle.
Continental Drift Theory
- Wegener’s hypothesis was that all the continents were once joined together in a single landmass and have since drifted apart. Wegener’s idea that the continents slowly moved over Earth’s surface became known as continental drift. According to Wegener, the continents drifted together to form the supercontinent Pangaea.
- Wegener gathered evidence from different scientific fields to support his ideas about continental drift. He studied land features, fossils, and evidence of climate change.
Evidence from Fossils
Fossil: Is any trace of an ancient organism that has been preserved in rock.
Wegener’s Hypothesis Rejected
- Wegener attempted to explain how continental drift took place. He suggested that the continents plowed across the ocean floors. Unfortunately, Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents. Because Wegener could not identify the cause of continental drift, most geologists rejected his hypothesis. Wegener said that if these geologists were correct, then mountains should be found all over Earth’s surface.
Mid-Ocean Ridges and Seafloor Spreading
Mid-Ocean Ridges
- The East Pacific Rise is just one of many mid-ocean ridges that wind beneath Earth’s ocean. In the mid-1900s, scientists mapped the mid-ocean ridges using sonar.
Sonar: Is a device that bounces sound waves off underwater objects and then records the echoes of these sound waves.
What is Seafloor Spreading?
- Harry Hess, an American geologist, was one of the scientists who studied mid-ocean ridges.
- Seafloor spreading continually adds new material to the ocean floor. In seafloor spreading, the seafloor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.