The Geological History of the United Kingdom

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• The Geological History of the United Kingdom

Natasha Lee University of Edinburgh
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• The UKs story really got started about 550
  million years ago, in a period of time geologists
  call the Cambrian
• At this time, Scotland and the rest of the UK
  were separated from each other by a large ocean
  called the Iapetus Ocean.
• Scotland sat near the Equator and was attached to
  North America and Greenland. England was attached
  to Africa, South America etc...and was actually
  floating around near the South Pole
• Russia and Scandinavia were plodding around on
  their own somewhere in between

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Cambrian period 550 million years ago
Iapetus Ocean
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In order to understand how the two countries came
together, we must first understand a little bit
about PLATE TECTONICS

• Remember those round boiled sweets that have
  different layers of colour moving from the centre
  to the edge? Well the Earth has layering just
  like that
• Inner core the middle bit. Its made of really
  hot, really squashed solid iron and nickel
• Outer core surrounds the inner core and is made
  of really hot liquid iron
• Mantle Surrounds the outer core and makes up
  most of the Earths volume. Its made of solid
  rock
• Crust the thin surface of the Earth that we
  live on.
• The crust generally not more than 100km thick.
  Thats quite thin when you think that the Earth
  is 6370km thick from core to crust (radial
  thickness)

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• The mantle is so hot that over millions of years
  it can flow by the process of convection. This is
  because the centre of the Earth is very hot, and
  convection is the best way to cool it down

Cold
Think of boiling water bubbling in a pan and
youve got convection currents... just like in
the mantle
Very hot
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• The Earths crust is divided into a number of
  segments, that we call tectonic plates.
• These plates contain OCEAN CRUST, which is heavy,
  and CONTINENTAL CRUST, which is light.
• Because of convection, all these plates are
  constantly moving. Where they meet, at PLATE
  BOUNDARIES, we get volcanoes and earthquakes

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Getting back to our story...

• 550 million years age, England broke away from
  Gondwana (i.e. South America, Africa etc...) and
  started the long journey north

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Cambrian period 550 million years ago
Iapetus Ocean
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Late Cambrian 500 million years ago
Iapetus Ocean
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Getting back to our story...

• 550 million years age, England broke away from
  Gondwana (i.e. South America, Africa etc...) and
  started the long journey north
• It did this by rifting and seafloor spreading.
  One of those mantle convection currents rose up
  underneath England and started pushing it away
  from Gondwana, leaving the Rheic Ocean behind it

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Making new crust at ocean ridges ...
4) Where these two PLATES split apart, volcanoes
erupt LAVA and make new crust.
3) Ocean crust above the mantle is dragged
sideways too
Oceanic crust
2) As the mantle cools, it stops rising and moves
sideways
Upper Mantle
1) Convection brings material up from the deep
Earth
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Getting back to our story...

• 550 million years age, England broke away from
  Gondwana (i.e. South America, Africa etc...) and
  started the long journey north
• It did this by rifting and seafloor spreading.
  One of those mantle convection currents rose up
  underneath England and started pushing it away
  from Gondwana, leaving the Rheic Ocean behind it
• As England moves north, the Iapetus Ocean gets
  smaller and the Rheic ocean gets larger

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Ordovician period 490-450 million years ago
Iapetus Ocean
Rheic Ocean
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Getting back to our story...

• 550 million years age, England broke away from
  Gondwana (i.e. South America, Africa etc...) and
  started the long journey north
• It did this by rifting and seafloor spreading.
  One of those mantle convection currents rose up
  underneath England and started pushing it away
  from Gondwana, leaving the Rheic Ocean behind it
• As England moves north, the Iapetus Ocean gets
  smaller and the Rheic ocean gets larger
• Eventually, the Iapetus Ocean disappears when
  England collides with Scotland during the
  Silurian period. Ironically, the geological
  boundary between England and Scotland is roughly
  where the modern geographical boundary lies!

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Silurian period 450-420 million years ago
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This is what happens when 2 bits of continental
crust collide...
2 continents are moving together
Rheic Ocean
Ocean crust is being formed here
When the 2 continents collide they stack up and
form mountains
Convection currents
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The Caledonian mountains 450 million years ago?

• The collision formed a massive range of mountains
  called the Caledonides
• These mountains may have been as high as the
  Himalayas
• The remains of these mountains are seen today in
  North America, Norway and ...

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...the Scottish Highlands
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After the collision....the Devonian period
(420-360 million years ago)

• Massive rivers start wearing away the Caledonian
  mountains, and deposit bits of ground-up rock and
  sand into huge valleys.
• Life on land is just getting started. Plants and
  trees start growing. We can find plant fossils
  of this age in Aberdeenshire

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Devonian sandstones

• The sand deposited from these rivers is turned
  into sandstone over millions of years.
• Sometimes these sandstones preserve fossil sand
  ripples like the ones you can see on a beach
  (only without the footprints)

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Devonian sandstones
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Devonian sandstones