Title: The Dynamic Earth
1The Dynamic Earth
2The Earth
What's inside the Earth?
3Structure of the Earth
4Plate Tectonics
5The World Today
6Science At Work Alfred Wegner
- In 1915 Alfred Wegner proposed a radical theory.
- He suggested that there was once a super
continent called Pangaea. - Pangaea then split up to form the continents that
we know today. - These then drifted into their current positions
7Pangaea 250 million years ago
Australia
8Pangaea to Now
9Pangaea to Now
10Pangaea to Now
11 Evidence - Migration of reptiles
12Evidence - Mountains
- The rock type, composition and formations of
mountains in eastern North America are similar to
those of mountains across north-western Europe.
13Evidence Coal
- Coal has been found above the Arctic circle.
- As coal comes from decomposed plants and it is
far too cold now to support plants, it must have
once moved from a warmer climate.
14Evidence Magnetic Alignment
- Although the magnetic alignments of ancient rocks
all point in different directions, they all point
in the same direction when the continents are
joined.
15Future Earth?
A
16Future Earth?
A
A
17Questions
- What evidence suggests that the continents were
once joined? - Correct these statements to make them true.
- Coal deposits above the Arctic Circle suggest the
land has floated there from warmer climates - Continents that do not have glaciers now have
always been too warm to have them. - Triassic reptiles could have swum the distances
required to populate different continents.
18Evidence from below
19World War II - Sonar
- During WW2 the military developed new technology
called Sonar. - This technology allowed the military to get
accurate maps of the ocean floor for their
submarines.
20Sonar Results
- Sonar revealed some interesting results
- That huge underwater volcanic mountain ranges run
down the centre of the oceans. - The ages of the rocks of the ocean floor vary
from brand new to 200 million years old. (this
is younger than the rock of the continents). - The rock of the continents is less dense than the
ocean floor and seems to float on it.
21Evidence Magnetic Stripes
Ridge
- The seafloor has been widely mapped by
magnetometers. As the oceanic plates grow the
magnetic zones form distinct stripes on the map.
This map is coloured according to the age of the
rocks - The stripes show that the youngest rock is next
to the ridges and the oldest next to the
trenches.
Red 0 9.7 mya Blue 126.7 180
mya Green 31 - 120 mya
mya Million Years Ago
22Magma and the Ocean
The ocean floor is a conveyor belt dragging new
rock from mid-ocean and in the trenches.
23- All the evidence suggests that the molten rock is
emerging along the mid-ocean ridges. - As the molten rock hits the water it cools,
building new mountains. - These new mountains push the old ones out of the
way. - The ocean floor acts like a conveyer belt,
carrying everything towards the trenches.
24Floating plates
25Inner Structure of Earth
- The earth is made up of layers we live on the
crust. - Next is the Mantle which is approx 2800 km thick.
26Keeping the mantle hot
- While the mantle tries to cool the crust helps to
keep the heat in. - Patches are also heated by the decay of
radioactive elements such as Uranium, Thorium and
Potassium.
27Convection currents
- Just as hot air and liquid rise, so will hot
liquid rock. Any rock over a hot patch in the
mantle will rise and cooler rocks will drop. - This cycle is called a convection current and it
takes millions of years to complete.
28Convection currents
29Questions
- What causes convection currents?
- How long do convection currents take to cycle
around the mantle? - What keeps the mantle from cooling down and
becoming solid?
30At the Edges
31Tectonic Plates and their Boundaries
32Types of Plate Boundaries
- There are three types of plate boundaries
- A) Divergent Each plate is moving away from the
other - B) Convergent Two plates that are moving towards
each other. - C) Transform The two plates are sliding past
each other.
33Example - Spreading
- As plates move apart they create cracks and form
rift valleys. - This allows hot magma to rise into the gap.
- This means old rocks are pushed out of the way as
the magma cools to form new rocks. - An example of two spreading plates are the
African plate and the Arabian peninsula.
Fact Some plates have been measured as moving
apart at a rate of 20cm a year!
34Spreading plates Another way of thinking about
it.
- Its like a wound (rift valley).
- A scab (Rock) begins to repair the wound but any
stress cracks it. - This allows blood (Magma) to ooze out.
- A new scab then needs to be made.
A Scab
35Science at Work Helgafjell Volcano
The Helgafjell Volcano Iceland
- The Helgafjell Volcano near Iceland is an example
where volcanic eruptions caused by two spreading
plates has created an island.
36Example Convergent
37Convergent plates form big mountains
- The Himalayas formed when the plate that carries
India collided with the Eurasian plate. - Both plates have similar densities and instead
of one going under the other they push against
each other. - This forms extremely large mountains.
38Example - Transform
39San Adreas Fault
- Transform boundaries are formed by plates
scraping against each other. - This doesnt make mountains or volcanoes, it
creates earthquakes. - The most famous transform boundary is the San
Andreas Fault. - This fault lies directly under San Francisco and
Los Angeles.
Fact Every year the coast of California moves
5cm this is making L.A closer to San Francisco
40Normal and Reverse faults
- Faults are lines of weakness in the earths crust.
- Normal faults are caused from movement away from
each other. The results is the formation of
cliffs and overhangs. - In reverse faults movement is towards each other.
This causes the two surfaces to overlap.
41Questions
- Can you think of an example of a land mass that
- That has broken away from the main mass of
Australia? - Outside of Australia?
- Label the boundaries on
- this slide
42What caused such destruction?
43Earthquakes
44Science at work Quake Lakes
May 14th 2006
May 15th 2008
May 19th 2008
- A satellite image shows the Yansai Lake forming
from a river at Tangjiashan in south-west China's
Sichuan province. This was the direct result of
an earthquake that devastated the region on May
12.
45Richter Scale
- The Richter magnitude scale was developed in 1935
by Charles F. Richter. - On this scale an earthquake registering a 6 on
the Richter scale is 31 times more powerful than
one registering a 5.
46Richter Scale
Richter Scale Measurement Earthquake effects
3 Felt slightly in areas near the epicentre
4 Felt by most people up to several kilometres from the earthquake. Some objects upset.
5 Strongly Felt. Some damage to weak buildings.
6 Moderately destructive. Some severe damage to weak buildings.
7 Major earthquake. Destruction of many buildings.
8 Very destructive. Total destruction of structures.
47Epicentre and Focus
- The focus is the point at which the earthquake
starts. - The epicentre is the point on the surface
directly above the focus of an earthquake.
48Seismic waves
- Seismic waves can be spilt into two categories
- Body waves which travel through the body of the
earth. These can be either - Primary (P)
- Secondary (S)
- Surface waves travel along the surface. These can
be either - Rayleigh (R)
- Love (L)
49Body Waves
- P waves are the fastest and are the first to be
recorded. This is because - P waves travel through solid and liquid rock.
- While S waves travel only through solid rock,
being stopped by liquid rock. Therefore they
travel along the surface.
50Surface Waves
- R waves are rolling waves. They are usually
quite small (1cm) - L waves arrive last and travel in an up and down
motion. - Together they cause cracks in the surface, which
then swallow and crush the objects above them.
51Science at Work Boxing Day Tsunami 2004
52How Tsunamis Happen
53How Tsunamis Happen
54Useful animations
- http//news.bbc.co.uk/2/hi/asia-pacific/5194316.st
m - http//news.bbc.co.uk/2/hi/science/nature/4126809.
stm
55Activity Earth Quake Tower
- Your task is to build a tower that will be able
to survive an earthquake. - You will have a limited amount of materials to
use so plan first! - The best tower team will win a prize.
56Volcanoes
57Volcanoes
58Types of Volcanoes
59Shield Volcanoes
Mauna Loa - Hawaii
- The biggest volcanoes are shield volcanoes.
- They get larger every time they erupt
- However their eruptions are more predictable and
less explosive.
60Composite Volcanoes
Mt Fuji
Mt St Helens
Mt Vesuvius
- Composite volcanoes are the most dangerous.
- They erupt explosively and violently.
- Examples are Mt Fuji (Japan), Mt St Helens (USA)
and Mt Vesuvius (Italy).
61Volcanos form islands
Krakatau, Indonesia
62Useful Website
- http//news.bbc.co.uk/2/hi/science/nature/4972366.
stm
63Mining
64Diavik Mine, Canada
This incredible mine can be found 300km northeast
of Yellowknife in Canada. (It's amazing that it
doesn't fill up with water, being surrounded by
it.) The mine is so huge and the area so remote
that it even has its own airport with a runway
large enough to accommodate a Boeing 737.
65Mirny Diamond Mine, Serbia
This mine is an absolute beast and holds the
title of largest open diamond mine in the world.
It is 525 meters deep with a top diameter of
1200 meters. There's even a no-fly zone above
the hole due to a few helicopters being sucked
in.
66Bingham Canyon Mine, Utah
This is supposedly the largest man-made
excavation on earth. Extraction began in 1863
and still continues today. The pit is constantly
increasing in size. In its current state the
hole is 3/4 mile deep and 2.5 miles wide.
67Kimberley Big Hole - South Africa
Apparently the largest ever hand-dug excavation
in the world, this 1097 meter deep mine yielded
over 3 tonnes of diamonds before being closed in
1914. The amount of earth removed by workers is
estimated to total 22.5 million tons.