plate tectonics (2) Flashcards
(52 cards)
Plate Tectonics
A theory which proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
Describe the view held by most geologists prior to the 1960s regarding the ocean basins and continents.
They believed that the continents didn’t move
Name the 20th century hypothesis that was at first rejected and then the theory that later replaced it.
Continental Drift Hypothesis
The Theory of Plate Tectonics
Continental Drift Hypothesis
A hypothesis, credited largely to Alfred Wegener, which suggests that all present continents once existed as a single supercontinent. Further, beginning about 200 million years ago, the supercontinent began breaking into smaller continents, which then “drifted” to their present positions
Supercontinent
A large landmass that contains all, or nearly all, of the existing continents
Pangaea
The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses
What was the first line of evidence that led earthly investigators to suspect that the continents were once connected?
Shape
Explain why the discovery of the fossil remains of Mesosaurus in both South America and Africa, but nowhere else, supports the continental drift hypothesis.
Its a freshwater reptile, it lived in lakes not in oceans
In the early 20th century view of how land animals apparently migrated across vast expanses of open ocean?
They walked across skinny land bridges or floated on rafts
Describe two aspects of Wegener’s continental drift hypothesis that were objectionable to most Earth scientists
Mechanism of continental drift
Continents were moving independent of oceanic crust
Theory of Plate Tectonics
A theory which proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
Lithosphere
The rigid outer layer of Earth, including the crust and upper mantle
Asthenosphere
A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 km and in some regions extends as deep as 700 km. The rock within this zone is easily deformed
Lithospheric Plate
A coherent unit of Earth’s rigid outer layer that includes the crust and upper unit
Divergent Plate Boundaries
Where two plates move apart
Convergent Plate Boundaries
Where two plates move toward each other
Transform Plate Boundaries
Where two plates grind past each other
What new findings about the ocean floor did oceanographers discover after World War II?
The seafloor is quite young, the sediment that was deposited was relatively thin-> seafloor is being recycle
Divergent Plate Boundary
A boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor
Ocean Ridge System
A continuous elevated zone on the floor of all the major ocean basins and varying in width from 500 to 5000 km. The rifts at the crests of ridges represent divergent plate boundaries.
Rift Valley
A long, narrow trough bounded by normal faults, It represents a region where divergence is taking place.
Seafloor Spreading
A hypothesis, first proposed in the 1960s by Harry Hess, which suggests that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence
Continental Rift
A linear zone along which continental lithosphere stretches and pulls apart. Its creation may mark the beginning of a new ocean basin
What is the average rate of seafloor spreading in modern oceans?
2 cm/yr in Atlantic
15 cm/yr in Pacific
Average: 5 cm/yr
