The Big Idea
Natural forces have been shaping our planet for many billions of years and these dramatic changes are
still going on, right now, all around us.
Throughout this unit we will be learning more about the physical processes that shape our planet – and
the vital role that we play in safeguarding our planet and its resources for future generations.
Explaining The Theme
In Geography, we’ll be finding out:
In International, we’ll be finding out:
The Big Picture
A sustainable environment - The Earth
The Earth is the third planet from the Sun. It is almost a sphere, but it is slightly flattened at the top and
bottom (the poles). We think of it as a solid rock; but it is more like a soft boiled egg. The hard shell is the
crust – a thin, rocky layer that is four-fifths covered in water. Beneath that is the white of the egg – the
mantle of mostly solid rock. In the centre of the Earth is the hot iron and nickel core, like the yolk of the
The Earth spins on its axis. Every twenty-four hours, it makes one complete rotation. It rotates anticlockwise,
seen from above. We call this complete turn a day. Part of the Earth is always facing the Sun.
This part is in daylight. But part will be facing away from the Sun. For this part of the Earth, it is nighttime.
As the Earth spins, each part of the Earth moves from light to dark and back to light again – from
day to night, and back to day.
From the Earth, it looks as though the Sun is moving across the sky. But it is the Earth that is turning,
while the Sun stands still. The Earth is going round the Sun. The time it takes to complete a full orbit is
365 and a quarter days – what we call a year. The quarters add together so that every four years, we have
an extra day in the year – February 29th. This 366-day year is called a Leap Year and February 29th is
Leap Year Day.
The Earth’s axis is at a slight angle to the Sun. This angle stays the same as the Earth orbits the Sun. Any
point on the Earth’s surface will spend some of the year leaning towards the Sun and in strong sunlight
and some of the year leaning away from the Sun. This is how we get our summer and winters.
Many planets have moons. Some have more than one. Jupiter, the largest planet in our solar system, has
63! The Earth only has one moon. No one knows for sure how the Moon came into existence. One theory
suggests that a huge rock hit the Earth about four billion years ago, sending a cloud of debris into space.
This debris got trapped in orbit by the Earth’s gravity, forming a ring. Over time, this debris would have
grouped into a ball.
The Moon is about one-eighth of the mass of the Earth. It orbits the Earth and also rotates on its axis.
Because it takes the same time to rotate as it does to orbit, one side always faces the Earth. This time is
about 27 days – roughly a month. As the Moon orbits the Earth, the Moon’s gravity pulls on the sea, giving
us the tides.
When we watch the Moon over a month, we see it appear to change in shape. These changes are called
the Moon’s phases. The Moon has no light of its own. It reflects the light of the Sun – even at night, when
the Sun is not in the sky. The shadow cast by the Sun means that the Moon appears to change in shape.
The Sun is a star – a massive ball of exploding gas. It measures about 1.4 million kilometres (approx.
875,000 miles) across and could hold more than a million Earths inside of it. However, compared to other
stars in the universe, the Sun is not that big at all!
The Sun is just one star out of billions in our galaxy, the Milky Way. Our own galaxy is just one out ofpotentially 500 billion galaxies in the universe. We really are just a very tiny speck in the vast expanse of
The Earth is one of eight planets, which orbit the Sun in our solar system. Like the Earth, they travel
around the Sun in near-circular orbits. The inner planets (those nearest the Sun) are: Mercury, Venus,
Earth and Mars. The outer planets (those farther away from the Sun) are: Jupiter, Saturn, Uranus and
Pluto was once considered the ninth planet in the Solar System. However, it is now considered a ‘dwarf
The Earth’s biomes
A biome is defined as a major regional community of animals and plants with similar life forms and
environmental conditions (for example, a tropical rainforest). There are six major biomes on Earth – arctic
tundra, evergreen forest, deciduous forest, grasslands, rainforest and desert. These biomes are a result of
the interactions between local geology, geomorphology and climate over millions of years.
These interactions determine landforms, soil and vegetation types, which in turn support specific types of
animals and also influence human activities. Plants, animals and human activity also influence soil types
and other natural processes.
An ever-changing landscape
Geomorphology is the study of landforms or the study of how the Earth is shaped by processes such as
glaciation, upheaval and erosion. Some processes are dynamically observable, such as a volcano erupting
– it can happen quickly. Some processes, such as changing coastlines and river courses, can be plotted
using a series of historical maps over decades. Other landform shaping processes, such as erosion by
water, are very slow, occurring over thousands of years.
The Earth is dynamic and ever changing: previous landscapes in the same place may have been vastly
different in prehistory. A quick look at the fossil record for a locality will show which creatures have lived
there in the past. As these creatures have specific climatic and vegetation needs then these must have
existed in this place at one time.
Pangaea – the supercontinent
It is through fossil records that scientists were able to show that many different continents – now
separated by ocean – once harboured the same plants and animals. This supports the theory that, 250
million years ago, the continents that we are familiar with today, were a single landform – a
supercontinent known as Pangaea (or sometimes referred to as Pangea). This continent broke apart
through the process known as ‘continental drift’. This ‘drift’ is still continuing today and will continue to
move continents apart or closer. In the future (approx. several hundred million years’ time!), North
America is predicted to collide with Japan and China.
What lies beneath
Geologists believe that the Earth is made up of four distinct layers. These are the: crust, mantle, outer
core and inner core.
The crust is the outermost layer of the Earth, often referred to as its ‘skin’. This is a made up of rock and
loose materials, which form our continents and ocean basins. The crust
is the thinnest of the Earth’s layers, approximately 8 km thick under the oceans (oceanic crust) and about
32 km thick under the continents (continental crust).
The mantle is the largest layer of the Earth, at nearly 2900 km thick. This layer is composed of very hot,
dense rock. Due to extreme differences in temperature from the bottom of the mantle to the top, parts of
the rock can move or ‘flow’. These currents cause the movement of the Earth’s plates, known as ‘plate
tectonics’ (see below).
The outer core is made up of super-heated lava, containing metals such as iron and nickel. This layer is
approximately 2,200 km thick. Due to the Earth’s rotation, the liquid outer core spins around the denser
inner core, causing the Earth’s magnetism.
The inner core lies at the very centre of the Earth. Here, temperatures and pressures are so great that the
metals of the outer core are squeezed together and forced into a solid. The inner core is about 1250 km
The Earth’s crust is broken up into pieces called plates. Due to changes in temperature in the Earth’s
mantle (the dense rock layer underneath the crust), convection currents can be generated. These currents
can move the plates.
The point where two different plates meet and interact is known as a boundary. There are three different
types of boundary:
Divergent boundaries – when the plates are moving away from each other. This movement can often
form volcanoes, as molten rock and gases escape from the ruptures in the crust.
Convergent boundaries – when two plates are being pushed together. As one plate pushes against
the other, one of the plates will be forced down beneath the other. This process can cause
earthquakes as well as the formation of mountain ranges.
Transform boundaries – when two plates slide against each other. This movement can generate large
amounts of energy, which is often released in the form of earthquakes.