week 3 - Continental Drift Flashcards
Alfred Wagner
Published the “Continental Drift” hypothesis in 1914. It suggested that the continents have moved and rotated over geological time.
Continental Drift
continents have moved and rotated over geological time
Alfred Wagner’s evidence for continental drift
- The apparent similarities of the coastlines of Africa and the South Americas
- Similar rocks on different continents
- Glaciation in places now located in the tropics
- Remains of Tropical plants in the Antarctic
- Fossil remains of plants and animals that lived in restricted areas but are now widely separated geographically
- Paleomagnetism (after Wagner)
Glacial deposition in hot regions
A glacial deposition (such as a boulder dropped by a glacier) in a hot region suggests that there must have been a once in a colder climate.
Land-based animals and plants in different areas
suggest that those areas have moved
Arthur Holmes
Provided Wagner with a mechanism to prove continental drift - called “Convection” - which marked the origin of the concept of the seafloor spreading
Harry Hess
In examining oceanic floors, hypothesized that the topography could be explained by the ocean crust splitting along the oceanic ridges called the “seafloor spreading”.
What explains topography of the ocean (mountain ranges)
The topography of the ocean (mountain ranges on the mid-ocean ridge) could be explained by the ocean crust splitting along the oceanic ridges called seafloor spreading.
Mid-Atlantic Ridge
Earth’s longest feature - 16,000 km long
The physical proof from continental drift comes from _______.
Paleomagnetism
Mechanism behind Paleomagnetism
Basalts and Gabbros are rocks that are rich in ferromagnesian minerals. Most Fe-bearing minerals are weakly magnetic at surface temperatures (magnetic as they cool below Curie Point) and solidify along the Earth’s magnetic field. These rocks retain their paleomagnetism until they are re-heated.
Mechanism behind Paleomagnetism
Basalts and Gabbros are rocks that are rich in ferromagnesian minerals. Most Fe-bearing minerals are weakly magnetic at surface temperatures (magnetic as they cool below Curie Point) and solidify along the Earth’s magnetic field. These rocks retain their paleomagnetism until they are re-heated. We can date the rock to determine how old it was.
Pillow Lavas
Rocks specifically formed under the ocean with a specific shape. They are volcanic rocks used to measure the past polarity of the earth’s magnetic field. Finding these rocks on land suggests that the land was once under the ocean.
Magnetic reversal
the Magnetic north has changed throughout geological time
Normally magnetized rocks
Rocks crystallizing at times when the Earth’s magnetic field was in the same orientation as today.
Reversely magnetized rocks
Rocks crystalizing when the field was oriented the opposite way from today.
Alternations of high and low _____ have been recorded to be symmetrical on both sides of the _____.
- Magnetism
2. Mid-Atlantic ridge
The bands closest to the Mid-Atlantic Ridge are ____.
Younger
A consequence of the spreading of the oceanic crust:
The older crust is farther from the ridge, and new lava filling the gap along the ridge becomes magnetized with the polarity of the earth’s magnetic field.
Declination
Measures the angular deviation between geographic (true) and magnetic earth.
Inclination
The direction of the earth’s magnetic field lines (it is possible to determine the magnetic latitude of a rock when measuring in 3D)
Polar Wonder Curve
Magnetized rocks of different ages may point to different apparent pole positions. This can make it appear as though the magnetic poles have moved in time - the continents have moved throughout time instead.
Pangea
A single large continent that broke up into the modern continents. Pangea existed approximately 300-200 million years ago.
Topographic maps of the seafloor show:
- There are ridges running N-S in both the Atlantic and Pacific oceans
- Along the margins of continents there are trenches several kilometers deep
- The continents are bounded by shallow water shelves
The rigid shell of the _____ is broken into pieces or plates. Each plate moves as a distinct rigid unit, riding on the _____ which is also in motion.
Lithosphere
Asthenosphere
Types of plate boundaries
divergent, convergent, transform-fault (slide horizontally past each other)
Distribution of earthquakes and volcanoes are also concentrated in belts, which directly correspond to edges of different _____.
Plates
Mohorovicic discontinuity
The boundary between the crust and mantle
Solid inner core
The innermost layer of the earth
Solid inner core
The innermost layer of the earth. 5140 km in radius deep.
Liquid outer core
The second most layer of the earth. At a radius of 5140 km to 2883 km deep.
Crust
The outermost layer of the earth. This contains the lithosphere.
Mesosphere
The middle layer of the earth. 2883 km deep to 350 km deep in radius. The layer is hot, but stronger, due to very high pressures.
Asthenosphere
The second outermost layer of the earth. It is 100 km to 350 km deep into the earth’s radius. This layer is hot, weak, and aplastic (has playdough-like consistency).
Lithosphere
The outermost layer of the earth. This layer is less than 100 km deep. This layer is cool, rigid, and brittle constituting the earth’s crust.
Earth’s internal layers
Solid Inner core, liquid outer core, mesosphere, asthenosphere, lithosphere
Difference between Continental crust and oceanic crust
Continental crust is less dense and is comprised more of Si and Al while Oceanic crust is denser and is comprised more of Fe and Mg
Chemical composition of the atmosphere
nitrogen and oxygen
Chemical composition of the hydrosphere
oxygen and hydrogen
Chemical composition of the crust
Oxygen, silicon, aluminum, iron, and magnesium
Chemical composition of the mantle
Oxygen, silicon, magnesium, and iron
Chemical composition of the core
Iron and nickel
What is the densest: continental crust, oceanic crust, mantle, or core?
Core > Mantle > Oceanic crust > Continental crust
Types of plate boundaries
Convergent, divergent, and transform
Convergent plate boundary
plates that are moving towards one another on a collision course. When plates collide, one is pulled into the mantle and recycled.
Divergent plate boundary
Plates that are separating from one another. At divergent boundaries, plates move apart and create a new lithosphere.
Transform plate boundary
Plates that slide past one another. At transform-fault boundaries, plates slide horizontally past each other.
What we know about the mechanism behind convection causing the plates to move
The lithosphere has the energy of motion and the source of this energy is Earth’s internal heat
Forces that play a role in moving brittle slabs of lithosphere around
- melting magma at oceanic ridges may push plates away from each other
- lithosphere breaks (and being relatively cool and dense) sinks through the less-dense asthenosphere pulling the plate along with it
- The whole plate may be sliding downhill away from the spreading ridges because the centre may be high on the seafloor
At greater depth, where temp and press are higher, rocks may behave more ___ and show more ___ behavior.
Plastically
ductile
____ behaviour is characteristic of most rocks at surface conditions, with low pres and temp.
Brittle
