THE THEORY OF SEA FLOOR SPREADING
THE THEORY OF SEA FLOOR SPREADING
THE THEORY OF SEA FLOOR SPREADING
Seafloor spreading: is a geologic process where there is a gradual addition of new
oceanic crust in the ocean floor through a volcanic activity where the old rock are
pushed above by the new injected rocks in the mid-oceanic ridge.
The theory of Sea Floor Spreading was developed by Harry Hess in 1960’s to support
the idea of continental drift theory. The Theory suggest that the ocean floor is now
spreading due to continuous eruption of molten materials from the mantle in to the
oceanic crust caused by plate tectonic movement. The main focus of the theory is to
discuss the formwtion of mountain ranges called mid oceanic ridges as a fundamental
result of plate tectonic movement. For example: The mid-Atlantic ridge System runs
parallel to the continental margins on the both sides of the Atlantic Ocean. Hess explain
that new crustal materials are being formed along the mid oceanic ridge s as the result
the motel materials are rising to the surface to form new oceanic crust by pushing
above the old rock.
CAUSES OF SEA FLOOR SPREADING
According to the theory, It has been suggested that to a large extent the sea floor
spreading is caused by radioactive elements. Normally, the radioactive elements such
as thorium and uranium in the upper mantle give off heat which is responsible for the
energy required which set up convectional currents. These currents move in a series of
cells throughout the upper mantle and asthenosphere. These currents rise under the
oceans, then move out horizontally in either direction, taking with them the continental
rafts of the lighter material in opposite directions and causing them to drift apart at
present rats of about 2.5cm a year. This would result in tensional rifts or cracks in the
ocean floor midway 64000km.
EVIDENCES OF SEA FLOOR SPREADING
Normally the most notably evidences of sea floor spreading are clearly observed on the
following regions:-
1. Presence of oceanic ridges: Thse refers to the sear floor mountains formed by plate
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tectonic movement. Usually they have about 2600 metres and risen about two
kilometers above the deepest part of ocean basin.
2. Presence of fractures and rifts at the mid oceanic ridge: There is deep rift valley at
the centre of mid oceanic ridge caused by the eruption of molten materials from the
mantle where the molten materials cools and become harder to form the new part of
ocean floor. The evidence of this scenario is the ocean florr of Atlantic ocean and Indian
ocean. The Atlantic ocean widens by 5cm per year.
3. Variation in age of rocks along the sea floors: The theory suggest that the rocks
found at the center of mid oceanic ridge are younger than rocks found the side of the
oven floor. Moreover the sea floor rocks are younger than continental rocks.
4. Magnetic evidences: The molten rocks with iron atoms moves with respect to the
magnetic poles. Therefore these rocks with different ages show different direction to
the magnetic poles. However magnetic poles differ with time in which rocks formed.
5. Presence of ocean trenches: This indicate the existence of subductionafter the sea
floor spreading. Example: Mariana Trench in the southern Pacific ocean.