Page 20 - Super Earth Encyclopedia

SPREADING RIFTS

Where the moving plates of Earth’s crust are pulling apart, they MID-ATLANTIC RIDGE
create spreading rifts that ease pressure on the hot rock below, The longest mid-ocean ridge runs from north
allowing it to melt. The molten rock wells up into the rifts, where to south along the floor of the Atlantic Ocean,
and is up to 1.8 miles (3 km) high. The original
it forms new crust. Most of these rift zones are on the ocean floor, rift began to form 200 million years ago,
where the heat beneath pushes them up into ridges of submarine in the early Jurassic age of dinosaurs. It has
been pulling apart at the rate of about 1 in
mountains. These mid-ocean ridges extend all around the planet, (2.5 cm) per year ever since, dividing
making them the longest mountain ranges on Earth. America from Europe and Africa.

North America

TRANSFORM FAULTS Transform The rift is
fault offset by the
The rift of a mid-ocean ridge transform fault.
does not form a continuous The ridge extends for about
9,900 miles (16,000 km)—
line. It is frequently interrupted from the Southern Ocean
by huge fractures in the oceanic to the Arctic Ocean.
crust. These transform faults
are caused by sections of
ocean floor moving away from
the rift in different directions.
Where a fault offsets the rift,
the rocks on each side of the
fault slide past each other,
causing earthquakes. Movement of
oceanic plate
Rising magma

HYDROTHERMAL VENTS
The central rift is flanked
The rift valley at the center of the ridge by transform faults caused
is dotted with hydrothermal vents—fountains by parts of the ocean floor
of superheated water that erupt from the moving in different ways.
hot rock. Minerals dissolved from the rock
by the very hot water turn to solid particles
in the cold ocean, forming white smokers South America
or sooty black smokers.

Thick continental
crust forms the
continent of
South America.

Extraordinary animals such
as these giant tubeworms Thin oceanic crust
form dense colonies forms the ocean floor
around the vents. of the South Atlantic. Ocean floor at the ridge is
raised by the expansion of hot
mantle rock below the crust.

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