seafloor spreading Flashcards
The mechanism that operates along the oceanic ridge system to create new seafloor.
seafloor spreading
The mechanism that operates along the oceanic ridge system to create new _____.
seafloor
Typical rates of spreading average around ______, roughly the same rate at which human fingernails grow.
5 cm/year (2 inches)
Comparatively slow spreading rates of ____ are found along the Mid-Atlantic Ridge, whereas spreading rates exceeding ______ per year have been measured along sections of the East Pacific Rise.
2 cm/year; 15 cm/year (6 inches)
The seafloor has a large _____ running through it. Deep trenches are found ___ from the ridges.
mountain range; far
The _________ of the seafloor changes.
magnetic polarity
The center of the ridge is of ______.
normal polarity
Stripes of normal and reverse polarity are found ______ on both sides of the ridge.
symmetrical
The rocks ____ to the ocean ridge were _____ than the rocks found further from the ridge.
closest; younger
This means that new rocks are formed at the ____ and push the older rocks away from the ridge based on the core sample collected from 1968, a drilling ship called the Glomar Challenger.
ridges
The seafloor has a large mountain range running through it. Deep trenches are found far from the ridges.
evidence of seafloor spreading
The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. Stripes of normal and reverse polarity are found symmetrical on both sides of the ridge.
evidence of seafloor spreading
The rocks closest to the ocean ridge were younger than the rocks found further from the ridge. This means that new rocks are formed at the ridges and push the older rocks away from the ridge based on the core sample collected from 1968, a drilling ship called the Glomar Challenger.
evidence of seafloor spreading
The ____ seafloor is much _____than the oldest continent.
oldest; younger
The oldest ocean floor rocks ever found are ___ million years old.
180
This proves that ocean floor is being ____ therefore all ocean floor rocks are ____ compared to the age of Earth.
destroyed; young
Rocks shaped like pillows (_____) shown that molten material has erupted again and again from cracks along the mid- ocean ridge and cooled quickly.
rock pillows
The oldest seafloor is much younger than the oldest continent. The oldest ocean floor rocks ever found are 180 million years old. Remember the Earth is 4.6 billion years old. This proves that ocean floor is being destroyed therefore all ocean floor rocks are young compared to the age of Earth.
evidence of seafloor spreading
Rocks shaped like pillows (rock pillows) shown that molten material has erupted again and again from cracks along the mid- ocean ridge and cooled quickly
evidence of seafloor spreading
Stripes in the seafloor. When magma cools, the iron cools into the mineral magnetite. It lines up parallel to the Earth’s present magnetic field. This iron is like compass needles, pointing north. So, when the rock hardens, a record of the Earth’s magnetic field at that time is locked in stone.
evidence of seafloor spreading
who pioneered the seafloor spreading theory
Harry Hess (1906-1969)
Harry Hess is a Former ____ Professor at ____ University
Geology; Princeton
Harry Hess was also a Head of Princeton’s _______
Geology Department
He was also the ____ of the Space Science Board of the National Academy of Sciences.
Chairman
It is a geologic process in which tectonic plates split apart from each other as a result of mantle convection.
seafloor spreading
It is a geologic process in which tectonic plates ____ apart from each other as a result of __________.
split; mantle convection
seafloor spreading occurs at ________
divergent plate boundaries
As tectonic plates slowly move away from each other, ___ from the mantle’s convection currents makes the crust __________
heat; more plastic and less dense.
The less dense material ____, often forming a ________ area of the seafloor.
rises; mountain or elevated
__________ are the elevated area on the seafloor
Mid-ocean ridges
how do mid-ocean ridges form?
-Crust cracks
-Hot magma fill the fractures and spills onto the crust
-Magma is cooled by frigid seawater.
-It forms igneous rock.
-This rock (basalt) becomes a new part of Earth’s crust.
-Subduction destroys old crust
-The two forces roughly balance each other, so the shape and diameter of the Earth remain constant.
Divergent boundaries can develop within a continent, in which case the landmass may ____ into two or more smaller segments separated by an ____
split; ocean basin
Divergent boundaries can develop within a continent, in which case the landmass may split into two or more smaller segments separated by an ocean basin
continental rifting
_______ begins when plate motions produce opposing (tensional) forces that pull and stretch the lithosphere.
continental rifting
Continental rifting begins when plate motions produce _______ forces that pull and stretch the lithosphere.
opposing (tensional)
Continental rifting begins when plate motions produce opposing (tensional) forces that pull and stretch the _____.
lithosphere
As the tectonic forces continue to pull apart the crust, the broken crustal fragments sink, generating an elongated depression called a _________, which eventually widens to form a narrow sea and then a new ocean basin.
continental rift
As the tectonic forces continue to pull apart the crust, the broken crustal fragments sink, generating an elongated depression called a continental rift, which eventually widens to form a narrow sea and then a new ______
ocean basin
Formation of the supercontinent Pangaea
200 mil yrs ago
Presence of the Panthalassan super ocean
200 mil yrs ago
Atlantic and Indian Oceans not present
200 yrs ago
Initial break-up of Pangaea and formation of Laurasia and Gondwanaland
180 mil yrs ago
Presence of an east-west trending basin (the Tethys sea)
180 mil yrs ago
Separation of Eurasian and North
140 mil yrs ago
the separation of north america and africa, which marked the opening of the north atlantic
150 mil yrs ago
American Plates
140 mil yrs ago
Onset of mid-Atlantic ridge development
140 mil yrs ago
Early formation of the North Atlantic
140 mil yrs ago
South Atlantic still closed
140 mil yrs ago
Separation of the African and South American Plates
80 mil yrs ago
Early formation of the South Atlantic
80 mil yrs ago
Indian plate reaches equator after separation from Australia and Antarctica
60 mil yrs ago
North and South Atlantic continue to widen
40 mil yrs ago
Onset of Indian and Asian Plate collision, initial formation of the Himalayas
60 mil yrs ago
North and South Atlantic achieve modern appearance
60 mil yrs ago
Major uplift of the Himalayas and formation of the Tibetan Plateau
20 mil yrs ago
Expansion of the Southern Ocean
20 mil yrs ago
Closure of mid-American seaway as North and South American plates collide
5 mil yrs ago
Isolation of the Pacific and Atlantic Oceans
5 mil yrs ago
