Continental drift
Starter
Which rock is the oldest?
Which rock is the youngest?
Dating rocks…
Those techniques can only tell you the relative ages of
the rocks. (Which ones are older than the others)
How can we actually tell how old they are?
Carbon dating
Half life
Radioactive dating…
Radioactive elements in rocks can be used to give an
estimate for their age. Scientists estimate the age by
measuring the amount of radiation that the rocks are
emitting. The earliest known rocks were dated using
radioactive uranium, which has a very long half life of
4.47 billion years, or potassium which has a half life of
1.25 billion years.
Dating rocks…
The radioctive decay of potassium
1
0.875
number of atoms
0.75
0.625
0.5
0.375
0.25
0.125
0
0
1.25
2.5
3.75
Time (billions of years)
5
6.25
Work to do…
Complete the worksheet on radioactive dating (p1_03_02)
to show your understanding of this technique.
Continental drift
Objectives
At the end of this lesson you......



must be able to state Wegener’s theory
should be able to describe supporting evidence for it
may be able to suggest reasons for peoples’
opposition to it
Mountain building…
100 years ago people thought that mountains were
formed as the Earth cooled and shrunk. They thought
this made the Earth’s ‘skin’ wrinkle like an apple.
They thought this wrinkling caused the mountain peaks
and valley troughs!
Mountain building…
When radioactivity was discovered in 1900, scientists
have realised that the heating effect of radioactive
materials inside the Earth actually prevents the Earth
from cooling and shrinking.
This means mountains couldn’t have been formed that
way!
A new method needed to be discovered (you’ll find out
properly how the mountains are formed next lesson but
for now lets consider the method that will lead to them
being formed)……
Alfred Wegener
In 1915 Alfred Wegener came up with a revolutionary new
theory about the continents and how the mountains were
formed. He suggested the continents had once been joined
together in the past and that they had slowly drifted apart
over millions of years!!!
At first nobody believed him....what do you think??
Can you see any
continents that
could have once
been joined
together?
Pangaea
Most people can spot
the match between
the shapes of South
America and
Africa. The two
continents look
like a piece of
a jigsaw. Alfred
Wegener. He looked
for fossil evidence
recorded in the rocks
to prove his theory.
How have the continents changed?
Moving continents?
Cut out the countries in the worksheet p1_03_03 and
stick them in your book to show Pangaea as Wegener
imagined it.
Make sure you label it ‘Pangaea’ and stick the key in as
well!
Work to do...
Complete page 1 of worksheet p1_03_01 continental
drift
Worksheet answers
Q2
Q3
India; Australia
For example, the shapes slotted into each other; the picture was
partly on one piece and partly on another piece; the colours/lines
matched.
Q4 Decide which shapes had matching outlines; decide which had ‘surface
evidence’ that matched.
Wegener’s story...
Video on Wegener and his discovery!
Wegener’s Summary
Wegener presented his idea of ‘continental drift’ to
other scientists in 1915.
He suggested that the plant and reptile fossils from
Africa and South America were identical. This must
mean there had to be a land bridge joining them. He
also found that the rock types and layers were also the
same.
He stated that the continents must have been joined
together and were moving apart slowly. He attributed
mountain building to the heating of the Earth and the
moving of continents.
Against Wegener?
Imagine that you are a scientist who was alive in 1915.
You have heard Wegener talk about his theory on
continental drift.
What problems are there with his theory?
Why do you not believe his ideas
• There are more simple explanations for some of
Wegener’s ideas.
• You can’t actually see the continents moving
• What force could actually move the continents?
Work to do...
Complete page 2 of worksheet p1_03_01 continental
drift
Wegener
Geologist
Explanation/evidence
The continents are moving
We can’t see continents
moving
If the continents take millions
of years to move, it would
be hard to detect
Continents may have moved
because of tidal movement
There is no evidence that
tides are strong enough to
move continents
Tides can’t move continents
but processes inside the
Earth could
Continents are shaped like
jigsaw puzzle pieces that
could be joined together
Continents have always been We need more evidence to
the same shape and don’t fit prove continents were once
exactly together
joined together
Fossils that lived in cold
climates can also be found in
continents that have hot
climates
Several continents were
clustered near the South
Pole and have now spread
across the Earth
The cold climate was more
widespread in the past
Mountains made from the
same rock types occur on
separate continents
Mountains formed in the
The same types of mountain
same way all over the Earth
are only found in some
as the Earth cooled and the
places on Earth
crust wrinkled
The same animals occur on
separate continents because
the continents moved apart
The same animals occur on
separate continents
There is no evidence of land
because all continents were
bridges but they can’t
linked by land bridges that
vanish completely
have now vanished
Plenary
Imagine you are telling your ill friend what they missed
today in class.
Summarise the lesson content into the three most
important sentences.