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Transcript of Earth
Earth
Earth
radius3957 miles
Earth: Then and Now•(4.6 Billion years ago)
Differentiation: Process that led to Earth’s layers; Denser materials like Iron sank to the center, and lighter materials rose to the crust
Earth’s Interior3 Compositional Zones
Crust-thin, outermost layer- varies in thickness-continental crust is thicker than oceanic crust
Mantle- middle layer- more dense than the crust
Core- central sphere- iron and nickel
Earth’s Interior
5 Structural Zones
Lithosphere- crust and upper mantle- rigid layer
Asthenosphere- less rigid layer of the mantle beneath the lithosphere- ‘plastic’ means that it flows very slowly
Mesosphere- Lowest part of the mantle- solid rock
Outer Core- liquid
Inner Core- solid
How do we know anything about the interior of Earth?
Kola Superdeep Borehole(1970-1989)
12,261m180° C
How deep can we drill into Earth?
CAT Scan
Using Seismology:
Earthquakes generate waves that travel through Earth and are recorded on the surface.
Exploring Deep EarthSeismology, Gravity, Geomagnetism
Seismometer
(real life)
Continental Drift:
The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations
Scientist: Alfred Wegener1912
15 major plates (and many smaller ones)
Pangea
Supercontinent that formed 300 million years ago and that began to break up beginning 250 million years ago
Evidence for Continental Drift• 1. Fossil Evidence
– Found small extinct land reptile fossils on both South America and Africa continent which had lived 270 million years ago.
• 2. Rock Formations– The ages and types of rocks in the coastal
regions of widely separated areas matched closely.
Identical fossils match up on different continents
Rocks and mountain formations match where continents used to meet
Evidence for Continental Drift• 3. Climatic Evidence
– Geologists have found glacier debris in Africa and South America suggesting they were once in a colder region. Plant fossils from the tropics at the poles.
• 4. Shape of the Continents– The Shape of the continents fit together like a puzzle
such as South America and Africa.
Several continents show evidence of having glaciers in the past
1858 Map – Continents fit together
Plate Tectonics
Plate tectonics is the theory that explains how large pieces of the lithosphere, called
plates, move and change shape.
How do they move around the planet?
Convection
Convection is the movement of heated material due to differences in density that are caused by differences in temperatures
Convection in everyday life
Evidence for plate tectonics
Locations of earthquakes
Locations of volcanoes
Mid-Ocean Ridges (MOR)
Oceanic crust was formed more recently than almost all continental crust, and the youngest of all crust is at
the MORs.
Seafloor spreading:
New oceanic lithosphere forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge
Magnetic reversals and magnetic symmetry:
Earth’s magnetic field has flipped direction in the past, meaning that sometimes magnetic
North is towards Earth’s North Pole and sometimes magnetic North is towards Earth’s
South Pole.
Newly formed ocean crust gets magnetized
Makes ‘Stripes’ of Normal and Reverse Polarity
‘Stripes’ symmetrical around mid-ocean ridge
North Geographic Pole: the point in the northern hemisphere where the Earth’s spin axis meets the Earth’s surface
North Geomagnetic Pole: the point in the northern hemisphere today where the pole of an imaginary bar magnet producing Earth’s field meets Earth’s surface
North Geographic Pole: top of Earth
North Geomagnetic Pole: where your compass points
Rocks with iron in them got magnetized by Earth’s field!
Paleomagnetism: studying magnetization of old rocks
Earth’s field sometimes flips (Reverses)
Types of plate boundaries
Divergent Boundaries
• Divergent boundaries occur when plate are rifted, or split, apart and begin to move apart.
• Creates large sections of oceanic crust. • Crust is created in this type of boundaries.
Off the coast of Central America
Convergent Boundaries
• Convergent means to converge, or bring together.
• Plate boundaries in which one plate (Oceanic) is pushed down under another (Continental) plate.
• Oceanic crust is destroyed at this type of boundary.
Off the coast of Chile
Oblique-Slip Boundaries
• Boundaries in which one plate slide past another with neither loss or creation of crust.
• San Andreas Fault• Also called “transform boundaries”
San Andreas Fault, California