C1bL12 Earth's Surface

Key Words

Canyon - a deep gorge dug out by a river.

Lithosphere - the crust and upper part of the mantle.

Mid-ocean ridge  - a long range of submarine mountains either side of a crack in the Earth's crust.

Pangaea - A single huge land mass formed from the present continents.

Sea floor spreading - Movement of the rock under the oceans outwards.

Supercontinent - a huge continental land mass, much bigger than what we have today.

Tectonic plates - huge slabs of the earth's surface fitting together like a jigsaw puzzle

Grade E

The Earth is an active planet.  Its surface is changing all the time, albeit very slowly:

• New mountains are being formed.  Mt Everest, 8868 m, was once at the bottom of a warm sea; it is limestone, and there are fossils even at the summit.
• Land is being eroded by water, and is washed into the sea.

People used to think that the Earth had always been the way it was, and the heat from the centre of the Earth is what's left over when the Earth was formed.

That is not the case

Grade C

The idea that there was a single supercontinent proposed in 1915 by a German geologist, Alfred Wegener.  His idea was not accepted at the time, and the First World War was raging.

                                                   Christian Darkin                                                       Tom van Sant                                                                             Christian Darkin

Pangaea (left hand picture) split up to form the land masses we see today (centre).  In the future, the land masses could look like the right hand picture.

 The Earth's lithosphere is split up into a number of interlocking tectonic plates:

Gary Hincks (Science Photo Library)

They move about on the convection currents in the Earth's mantle.  The rate is slow, about the rate your fingernails grow, but the forces are massive leading to:

• Mountain building;
• Earthquakes;
• Volcanoes.

The Alps formed when two plates collided, crumpling the land like a huge slow-motion car accident.

Grade A

If you look at the Earth's plates, you will see a long crack passing along the length of the Atlantic Ocean.  This is a mid-ocean ridge, where plates are moving apart.  The crack is filled all the time with molten lava which rapidly cools under the cold water.  The pressure is so great that no steam is formed by the hot water surrounding the rocks.

Dr Ken MacDonald

Around the mid-ocean ridge you will find:

• Fissures (cracks in the ocean floor) as in the left hand picture;

• Smokers - strange looking vents from which columns of mineral rich water emerge,  The water is very hot.

• Very strange looking animals.

Fewer people have explored the very deep ocean than have been into Space.

Seafloor spreading occurs at a rate of about 2.5 cm a year.  So you are 40 cm further away from the United States than when you were born.