Asthenosphere/Mesosphere Asthenosphere – the soft layer of the mantle on which tectonic plates move. Mesosphere – the strong, lower part of the mantle.
Types of Crust 2 Types of Crust - continental: the lighter, older, and thicker part of the crust that makes up the continents. - oceanic: the rock that forms the ocean floor.
Tectonic Plates Tectonic Plates – pieces of the lithosphere that move around on top of the asthenosphere.
Earth’s Layers-Mantle Mantle – the layer of Earth between the crust & the core. - much thicker than the crust. - contains most of the Earth’s mass. - more dense than the crust.
Earth’s Layers-Core Core – the layer of Earth that extends from below the mantle to the center of Earth. - made mostly of iron. - makes up 1/3 of Earth’s mass.
Parts of the Core Inner Core – the solid, dense center of Earth. Outer Core - the liquid layer of the Earth’s core that surrounds the inner core.
END OF NOTES END OF EARTH’S LAYERS NOTES!!
The Theory took off in the early 1960’s and started a revolution in Earth Science! It Unified the study of Earth Science Provided explanations to ancient questions: (1)Why do earthquakes/volcanoes occur in very specific places on Earth? (2) How are great mountain ranges like the Alps and Himalayas formed?
Wegener’s Theory of Continental Drift had a fatal weakness: It couldn't answer the fundamental question: What kind of forces could be strong enough to move such large masses of solid rock over such great distances?
Wegener’s answer: The continents simply plowed through the ocean floor!
Four major scientific developments had to happen after Wegener's death before his theory gained acceptance.
The First Discovery 1.Demonstration of the young age and ruggedness of the ocean floor.
Plate Tectonics 1. Scientists discovered right after World War II: The Atlantic Ocean floor is not flat! It has a huge mountain chain down the middle, now called the Mid-Atlantic Ridge!
1.Scientists also discovered: The oldest continental rock is 4 billion years. BUT: The oldest ocean floor rock is ONLY 200 million years.
2. Reversals of the Earth’s magnetic field on the ocean floor near the Mid-Atlantic Ridge The Second Discovery
Draw this on your paper: Mid-Atlantic Ridge 5 mya 10 mya 0 mya
The Third Discovery 3. Seafloor Spreading Theory which introduced the concept of the recycling of the oceanic crust. New magma rises through the ridge and new oceanic crust is created…
3…then the old crust plunges down into the Asthenosphere, melting back into new magma...
Seafloor Spreading is caused by Convection Currents in the Asthenosphere. Hot water, air, and magma rise because of low density and sink because of high density.
Seafloor Spreading The plates are dragged along like a Conveyor Belt (“Slab-Pull”).
The Fourth Discovery 4. The precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and ridges.
Earthquakes and Volcanoes are concentrated along Lithospheric Plate boundaries.
Once these discoveries were made: Wegener’s Theory of Drifting Continents was accepted by scientists because we could explain how continents moved.