MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 8ga1
8Ga1 Looking at rocks
Name _____________________________ Class ____________
Rock
Colour
Size of grains
Are the grains shiny?
Do the grains fit together?
Sketch of rock texture
[observing]
8Ga2 Porous rocks 1
Which rock is the most porous?
If a rock has rounded grains, water can get into the gaps between the grains. Rocks like this are said to be porous. You can find out how porous a rock is by finding how much water it will absorb.
Apparatus
- Rock samples
- Hand lens
- Beaker
- Balance
- Paper towels
Method
1 Write the names of your rock samples in the table on the next page.
2 Examine the samples carefully using the hand lens. Predict which rock will absorb the most water and which will absorb the least. Write your predictions in the spaces below.
3 Find the mass of each rock sample. Write the masses in the 'dry mass' column in the table.
4 Put the rock samples into a beaker of water. Leave them for 10 minutes.
5 Take the rocks out of the water, and dry them using paper towels. Find the masses again, and write them in the table.
6 Work out how much water each rock has absorbed, by taking the dry mass away from the mass after soaking.
7 Now divide the mass of water by the dry mass of the rock.
Prediction
I think that __________________________ will absorb the most water, and _________________
__________________________will absorb the least.
Recording your results
Dry mass (g)
Mass after soaking (g)
Mass of water absorbed (g)
Mass of water
Dry mass of rock
Considering your results/conclusion
I have found that __________________________ absorbs the most water. This is because it has
_____________________________________________________________________________ .
My prediction was ______________________________________________________________ .
Evaluation
Why do you think you had to divide the mass of water absorbed by the dry mass of the rock?
_______________________________________________________________________________
[ predicting, observing, considering, evaluating ]
8Ga3 Porous rocks 2
1 Examine the rock samples carefully using the hand lens. Predict which rock will absorb the most water and which will absorb the least.
Planning
2 You will need to find the mass of each rock sample before and after soaking it in water, and then divide the mass of water absorbed by the dry mass of the rock. Write a short method for your investigation.
3 Draw a table for your results. Include enough columns to show the results of the calculations you will need to do.
4 Record your results in your table, and carry out any calculations.
5 Why did you need to divide the mass of water absorbed by the dry mass of the rock?
6 Which rock absorbed the most water?
7 Why do you think this rock absorbed the most water?
8 Was your prediction correct?
9 Was your experiment a fair test? Explain your answer.
10 Are there any improvements you could make if you had time to repeat the experiment?
[ planning, observing, presenting, considering ]
8Ga4 Mohs' Scale of Hardness
You can file your fingernails, because the nail file is harder than your nails. The nail file scratches your nails, but you cannot scratch the file.
You can find out how hard a mineral is by seeing which minerals it will scratch. A mineral will scratch any minerals that are softer than it is. We can use this idea to test minerals, even lumps of very soft minerals like talc (when it is crushed up, this gives us talcum powder!).
- Mineral samples
1 Choose two minerals, and scratch one mineral with the edge of the other mineral. Swap them over and try again.
2 Look at your minerals. Have you made a scratch on either of them? Which mineral scratched most easily? Which of these two minerals is the hardest?
3 Now try other pairs of minerals.
Look at all your results, and write a list of the rocks you have tested in order of hardness.
Using Mohs' Scale
If you only have one or two mineral samples, you can still find their hardness using Mohs' Scale of Hardness.
1 Describe how to find out which of two minerals is the hardest.
2 If you wanted to scratch every mineral on Mohs' scale, which mineral would you use? Why?
3 If you wanted to use a mineral which would not scratch any other mineral, which one would you use? Why?
4 Why do we make tools like spades, saws and knives out of iron or steel, and not out of wood?
5 Imagine you are a builder.
a What would be the advantages and disadvantages of using a soft material to build a house?
b What about a hard material?
[ observing, considering ]
8Ga5 Describing rocks 1
A B C D
not to scale
Rocks are mixtures of minerals. The grains in rocks can be different shapes and sizes. Interlocking grains (crystals) fit together without any gaps between them. If the grains are rounded, there can be gaps between the grains and the rock may be porous. Porous rocks can absorb water.
1 Which two rocks have interlocking crystals?
2 How many different kinds of mineral are there in:
a rock A
b rock B
c rock C
d rock D?
3 Which rock is made of rounded grains that are all the same size?
4 Which rock is made of several different sizes of rounded grains?
5 Which two rocks are porous?
6 Which rock do you think will absorb the most water? Explain your answer.
7 Read this description of granite.
'Granite consists of three main minerals. One of the minerals often forms large crystals.'
Which rock could be granite?
8 Read this description of conglomerate.
'Conglomerate is made of quite large, rounded pebbles, in a mixture of much smaller grains.'
Which rock could be conglomerate?
[ knowledge ]
8Ga6 Describing rocks 2
1 Look carefully at the drawings of rocks. Describe the texture of each rock in as much detail as you can. Remember to include the following information:
- shape of grains, and whether or not they interlock
- size (or sizes) of the grains
- how many different kinds of mineral you can see.
2 Write a list of the rocks in order of porosity. Explain why you have put the rocks in that order.
Conglomerate consists of rounded pebbles set in a mixture of finer grains.
Sandstone usually consists grains of quartz that are all of similar size.
Granite consists of interlocking grains of feldspar, mica and quartz. The grains are usually greater than 2 mm in size, and feldspar can develop into much larger crystals.
3 a Which rock is sandstone?
b Which rock is conglomerate?
c Which rock is granite?
4 Use information from the text above to work out the names of each of the minerals W, X, Y and Z. (Hint: Two of these minerals are the same.)
8Ga7 Rocks from space
'Shooting stars' are not stars at all - they are pieces of rock, called meteors, which fall into the Earth's atmosphere. Friction with the air heats them up so much that they glow, and most of them burn up. The pieces of rock that are big enough to survive their fall and land on the Earth are called meteorites. It is estimated that over 20 000 meteorites with a mass of greater than 100 g fall to the ground every year. Most of them fall into the sea or into deserts, and only a few are found by scientists.
Scientists think that most meteorites are fragments of rock from the asteroid belt, but there are a few that have come from Mars or the Moon. They are bits of rock that were thrown up from Mars or the Moon when an asteroid or a comet hit it, millions of years ago. Scientists did not believe at first that a piece of rock from another planet or the Moon could be thrown up high enough to leave the planet or the Moon permanently. However, when they compared a lunar meteorite (one from the Moon) with moon rocks, they found that the meteorite definitely came from the Moon.
1 a What are shooting stars?
b Why do you think they are called shooting stars?
2 Why do most meteors never reach the surface of the Earth?
3 What is the difference between a meteor and a meteorite?
4 Why do scientists only find a few meteorites each year?
5 a What piece of evidence convinced scientists that some meteorites could have come from the Moon?
b What year was the earliest that this evidence could have been collected? (Hint: You will need to find out when the first people visited the Moon.)
6 Why do you think scientists are interested in studying meteorites and what they are made of?
[ literacy, research ]
8Gb1 Scenery 1
Different parts of the country have different kinds of scenery, because of the different kinds of rock that make up the land.
Dartmoor and Bodmin Moor, in south west England, are areas of high ground made from granite. In some places piles of rocks or boulders stick out above the ground, as tors.
Complete these sentences using words from the box at the bottom of the page. You will need to use some words more than once.
Tors are made of a rock called _________________ .
This rock usually has some _________________ in it.
Rain _________________ can get into the cracks.
Rainwater is slightly _________________ , and it reacts
with the _________________ in the granite. This is known
as _________________ weathering.
Chemical _________________ happens along the cracks.
The _________________ get bigger. Some pieces of granite
fall off, forming _________________ .
The_________________ material gets washed away.
The _________________ has mostly broken up into
boulders. This is a _________________ .
acidic boulders chemical cracks
granite minerals tor water
weathered weathering
8Gb2 Scenery 2
Dartmoor and Bodmin Moor, in south west England, are areas of high ground made from granite. In some places the rocks stick out above the ground, as tors.
Rainwater gets into the cracks. The rock is weathered.
Rounded granite boulders are left sticking out of the ground. This is a tor.
Tors are formed by the chemical weathering of granite.
Many parts of Yorkshire are made of limestone. Limestone reacts with acidic rainwater to form soluble salts, which get washed away. Limestone pavements form when rain reacts with the limestone along cracks in the rock. Limestone often contains cracks, so there are not usually many streams in limestone country.
Limestone pavement
1 What kind of rock is found on Dartmoor?
2 What are tors?
3 The diagrams at the top of the page show how tors are formed. Describe in words how tors are formed.
4 What shape do you think the rock would be weathered to if there were no cracks in it? Explain your answer, and draw a sketch to help you explain.
5 Which do you think would take longest to form: a tor or a limestone pavement? Explain your answer.
6 Why are streams usually rare in limestone country?
[ knowledge, literacy ]
8Gb3 Limestone scenery
Landscapes formed on limestone, like the Yorkshire Dales, have several distinctive features that are not seen anywhere else. These features occur because limestone reacts with slightly acidic water, and often has lots of joints (cracks) in it.
Sinkholes are places were streams disappear into cracks in the limestone. Dolines are dips or openings in the ground. Solution dolines are formed as rainwater seeps down through the soil and then starts to dissolve the limestone underneath, forming a drainage outlet at the bottom. Collapse dolines form when rock collapses into a cave beneath. Subsistence dolines or shakeholes form when soil is washed down a crack in the rock, and a dip in the grass surface is formed.
1 How do you think the sinkhole and caves formed?
2 Look carefully at the diagram. Which kind of feature are A, B and C? Explain your reasoning.
3 Describe what you would see if you stood near:
a a sinkhole
b a spring
c a shakehole.
4 Look carefully at the layers of shale shown in the diagram. Write down two differences in the properties of shale and limestone.
5 How would the diagram above be different if it was drawn in a thousand years' time? Either describe the differences, or draw another diagram to show the differences. Explain your reasoning.
6 Find out what clints and grykes are and how they are formed.
[ knowledge, literacy, research ]
8Gc1 Best rock for a statue 1
What is the best rock for making a statue that will last for years?
- Samples of different rocks - Plastic beaker - Eye protection
- Dilute sulphuric acid - Balance - Paper towels
- Bowl for used rock samples - Large iron nail
Complete these sentences using the words in the box below and some of your own to describe what you are going to do.
1 Appearance
A statue should look nice, so I would like to make the statue out of _______________ rock.
I think this will look the best because ___________________________________________ .
2 Toughness
I will test the rocks to see how tough they are by _______________ my finger over the rock
to see if any of the rock _______________ off. I will try to scratch the rock using a metal
_______________ to see how tough the rock is.
3 Reaction with acid
I will put the rock into some dilute _______________ to see if
the rock and acid react. This will tell me if the statue would be
damaged _______________.
Wear eye protection.
4 How much water does it take up?
I will find the mass of my piece of rock using a _______________ and then put it in a beaker
of water for 5 minutes. I will dry off any extra water and then find the mass again. This will
tell me how much _______________ the rock soaks up.
acid acid rain balance falls nail rock rubbing water
Write your results in the table below.
Name of rock
Appearance - what does rock look and feel like?
Hardness
Reaction with dilute acid
How much water does it absorb?
My results tell me that the best rock to use would be ________________ . This is the best rock
because ________________________________________________________________________
______________________________________________________________________________ .
8Gc2 Best rock for a statue 2
There are several features of the rock that you should consider:
- What colour and texture will the rock have when the statue is made?
- How difficult will the rock be to carve into shape?
- Will the rock be damaged by acid rain? If so, will this matter?
- What will happen to the statue when it gets wet?
- Will the rock be damaged by changes in temperature?
1 Plan a series of safe experiments to help you gather information about each of the rocks you have available. Remember to include these things:
- the apparatus you will need
- how you will carry out each test
- how you will make sure your tests are fair
- how you will make sure your tests are safe.
Show your plan to your teacher before carrying out your experiments.
2 Record your results in a table.
Considering your results/conclusions
3 Which rock would you use for your statue? Explain why you chose this rock.
4 Is there any way you could improve your tests if you had time to do them again?
[ planning, observing, presenting, considering, evaluating ]
8Gc3 Physical or chemical weathering?
When chemical weathering happens, a rock reacts with a chemical such as acid in rainwater. A new substance is made.
When physical weathering happens, no new substances are made. The rocks do not change into a new substance, but they are
Biological weathering is when living things cause rocks to break apart or wear away.
For each diagram, decide what is causing the weathering, and if it is an example of chemical, biological or physical weathering. Fill in the gaps in the sentences using words from the box. You may need some words more than once.
1 _______________ changes can cause
_______________ weathering. The rock
_______________ during the day when it
is hot and contracts when it is
_______________ at night.
2 _______________ roots can cause
_______________ weathering. The plant
_______________ grow into small
_______________ in the rocks, and push
the sides of the cracks apart when they
_______________ bigger.
3 _______________ - _______________ action can
cause _______________ weathering.
Water in in the rock expands when it
_______________ and makes the crack bigger.
4 _______________ can cause _______________
weathering. The _______________ in the
rain dissolves parts of the rock. This process is
speeded up if the rain contains a lot of acid.
Rain like this is called _______________
_______________ and can be caused by burning
_______________ fuels.
acid biological chemical cold cracks expands
fossil freezes freeze-thaw grow physical plant
rain roots temperature water
8Gc4 Out in all weathers!
Rocks in the UK are mainly weathered by freeze-thaw action or by chemical weathering. The amount of weathering depends on the weather conditions. The maps below show the average rainfall per year in the UK, and the average number of days per year when it is frosty.
Average rainfall per year*
Number of nights with frost*
Look at the maps carefully and use them to help you answer the following questions.
1 Which area has the highest average rainfall?
2 Which area has the lowest average rainfall?
3 Frost happens when water in the air freezes. Which area gets the most frost?
4 Which areas do you think suffer the most chemical weathering? (Hint: Remember that chemical weathering is caused by rain water.)
5 Which area do you think suffers the most weathering by freeze-thaw action? Explain your answer.
The stone that this cottage is made from will be changed by weathering.
6 Describe how the stone could change and what types of weathering will cause these changes.
7 Imagine that you could build this cottage in any part of the UK. Which area would you choose to build in, if you wanted the cottage to last for hundreds of years? Use information from the maps to help you explain your answer.
[ numeracy, knowledge ]
8Gc5 Heating and cooling
Repeated heating and cooling of rocks can cause cracks to form. This often happens in desert areas where there are large temperature changes between day and night.
During the day, the outer part of the rock heats up more quickly than the inside, and expands. At night, the outer part of the rock cools and contracts. The continual expansion and contraction eventually causes cracks in the rock.
Some of the cracks are parallel to the surface, and some are at right angles to it. The outer part of the rock breaks into layers. This kind of weathering is sometimes called exfoliation.
1 Why doesn't the whole rock heat up during the day? Use the word 'conductor' in your answer.
2 The cracks parallel to the surface are caused by the expansion of rock during the day. Look at the diagram above, and write an explanation of how this happens.
3 Explain how the cracks at right angles to the surface are formed. Use diagrams similar to the ones above to help you to explain.
Water can get into cracks in rocks. When water freezes, it forms ice. Ice is a very unusual solid. Most solids contract as they cool down, but as water cools down from 4 °C to 0 °C, it expands. A lump of ice has a bigger volume than the liquid water from which it was made.
4 Draw a series of labelled diagrams to explain how freeze-thaw weathering happens.
5 Physical and chemical weathering happen at different rates in different parts of the world. They depend on the maximum temperature (chemical reactions happen faster when it is warm), the minimum temperature, the temperature difference between day and night, and the amount of rainfall. Which combination of conditions would make these types of weathering happen fastest? Explain your answers.
a chemical weathering
b freeze-thaw action
c exfoliation
8Gd1 How far are grains carried? 1
Label the diagram below and fill in the gaps in these sentences using words from the box.
We used a piece of ________________ to make a model of a stream. We put some damp
________________ and gravel in the bottom of it. We placed the guttering so that one end was
________________ than the other. We put a large ________________ under the bottom end so that
it caught the ________________ . We used a thin pipe to let water into the top end of the guttering
and watched what happened to the sand.
We changed the ________________ of the water by making one end of the guttering higher or
________________ .
guttering higher lower pipe sand speed trough water
When the water flowed slowly, ________________ (big/small) grains were not carried very far.
Only the________________ (largest/smallest) grains were carried by the water.
If the water flowed ________________ (faster/slower), then bigger grains were moved by the water.
Fast moving water can carry ________________ (bigger/smaller) grains than ________________
(fast/slow) moving water.
8Gd2 How far are grains carried? 2
- Guttering - Trough - Damp sand - Gravel
- Plastic pipe - Water - Access to sink - Stop clock
You can make a model of a stream in the laboratory by using a piece of guttering and a large trough. This is called a flume. The guttering should be raised at one end and have a layer of sand along its length. Water is allowed to run from the top of the guttering down into the trough. The trough should be placed in a sink so that the overflowing water can go down the drain without taking the sand with it.
1 First, record what happens to the sand when a stream of water is allowed to flow down the guttering. Try to explain why this happens.
2 Use your observations about this experiment to decide on a question that you would like to investigate further.
3 Write a plan for your investigation, making sure that you include all of the following points:
- what you want to find out
- what you think will happen
- why you think this will happen
- how you will change the experiment so that you can find the answer to your question
- what you will measure and record
4 Show your plan to your teacher to make sure that it is safe before you start your investigation.
[ planning, predicting, observing ]
8Gd3 Moving grains 1
Fill in the gaps using words from the box at the bottom of the page. You may need some words more than once.
1 Chemical and ________________ weathering attack rocks. Rock fragments break off and ________________ to the bottom of the cliffs. Some rocks roll down the slope into streams or ________________ .
2 Rock fragments are ________________ (carried away)
by the river. Big rocks do not move very far, but
________________ grains can be moved a long way. The
rocks ________________ into each other and get
________________ away. This is called
________________ . The pieces of rock in the river get
smaller and smaller.
3 When a river flows into a ________________ or the sea
it ________________ down. The water cannot
________________ all the rock grains, so they are
________________ (fall to the bottom) and form a layer
of ________________ .
abrasion bump carry deposited fall lake physical
rivers sediment slows small transported worn
[ literacy ]
8Gd4 Moving grains 2
Grains of rock can be transported by wind as well as water. If a mixture of large and small grains are dropped into a stream of air (wind), then some grains will be carried further than others. This process is also used to separate heavy grains of wheat from the lighter chaff when wheat is harvested (the chaff is bits of dried stalk and seed coverings).
1 Which do you think will travel further on the wind, the grains of wheat, or the chaff? Explain your answer.
2 Do you think all of the wheat will travel the same distance? Explain your answer.
3 Will all the bits of chaff travel the same distance? Why?
4 If the wind blew over a pile of sand and dust, which would get blown the furthest? Why?
5 Look at the five different sized fragments of rock, labelled A, B, C, D and E in the drawing.
A B C D E
They would be carried different distances by a river. Put them in order, starting with the one that will move the furthest. Explain how you worked out your answer. (Draw a diagram if it helps you to answer the question.)
6 Rivers are always full of muddy water after a storm. Why do they look so muddy? Where has the mud come from? (Hint: Rivers usually flow faster when there is a lot of water in them.)
7 When the water level drops again after the flood, layers of mud are left in the areas that were flooded. Explain why this mud has been left there. (Hint: Think about what happened to the speed of the river as the water level dropped.)
8 When the storm is over, and the water level returns to normal, the water in the river becomes clear again. Explain why.
8Gd5 On ice
Rock fragments can be moved by ice as well as water. The UK has been covered by sheets of ice many times in the past. The last ice sheet to cover most of the UK covered Scotland, Wales and most of northern England and northern Ireland, and melted about 13 000 years ago. About 2000 years later another cold spell caused ice caps to form in the highlands of Scotland, and small glaciers to form in the mountains of Wales and the Lake District.
The ice sheets moved slowly, and carried rocks and stones with them. Some large stones or boulders can be moved hundreds of miles by ice. When the ice melts and the boulders are left behind, they can be identified because they are usually made of a different type of rock from the underlying bedrock. Rocks like this are called erratics. In the UK, boulders of granite from Shap (in Cumbria) can be found as far east as Robin Hood's Bay on the Yorkshire coast.
As the ice sheets move, rocks stuck in the bottom of the ice scrape across the land and wear it away. Many valleys in the mountainous areas of the UK were carved out by glaciers, and have a characteristic U shape.
Erratics are sometimes found perched on pieces of the underlying rock which have been worn away.
1 When was the last ice age that covered most of the UK?
2 Why do you think the most recent cold period only caused glaciers to form on high ground?
3 Which can carry the largest rocks: glaciers or rivers? Explain your answer.
4 What is an erratic?
5 Look at the drawing of an erratic. What can you say about the properties of the erratic compared to the rock it is resting on? Explain your answer.
6 How far has a Shap granite erratic been moved if it is found at Robin Hood's Bay? You will need to use an atlas to work out your answer.
7 Choose two of these features and find out what they are. Describe how they were formed, using diagrams if necessary. Choose from: hanging valleys, kettle holes, corries/cirques, moraines.
8Ge1 Key ideas
Cut out these cards, and match them up into pairs. Stick the correct pairs into your book.
[ knowledge, revision ]
------------------------------------------------------------------------------------------------------------------------------
Rainwater is slightly acidic, and can react with the minerals in rocks.
Remains of plants and animals sometimes get buried in sediments and can form fossils.
When the roots of plants get bigger they can crack rocks apart.
Mud and sand are deposited as the river slows down.
Stones bump into each other as they are carried along by water, and become smaller and more rounded.
Water gets into cracks in rocks and expands when it freezes, eventually breaking rocks apart. Rock fragments fall to the bottom of cliffs.
8Ge2 Rocks revision
Complete these sentences using words from the box.
acidic animals big bump cracks deposited evaporates
expands fossils freeze-thaw grains interlocking layers
minerals physical porous react rocks shape temperature
transported water weathering worn
Rocks are made up from mixtures of ________________ . The
texture of a rock depends on the size and ________________ of
the grains. Rock A has ________________ grains. Rock B has
rounded ________________ . Rocks like this are often
A B
Rain is naturally ________________ , and can react with the minerals in ________________ .
Some rocks, like limestone, will slowly ________________ with rainwater. This is called chemical
________________ . ________________ weathering is caused by changes in ________________ .
Temperature changes have bigger effects when
________________ gets into cracks in rocks. Water
________________ when it freezes, and can widen the
________________ . This is called ________________
________________ action. Rock fragments can be
________________ by flowing water. Small fragments are carried further than ________________
ones. The rock fragments ________________ into each other and get ________________ away
while they are being transported. The rock fragments are ________________ when the river slows
down. Sediment often forms ________________ . Sediment can also be formed when water
________________ and leaves salts behind. Parts of dead plants or ________________ can
sometimes be preserved as ________________ .
[ revision, literacy ]
8Ge3 Rocks crossword
Fill in the correct words on the crossword grid, using the clues below.
1
2
3
4
5
6
7
8
9
10
11
12
Across
2 This kind of weathering happens when ice forms in cracks in a rock.
8 Rainwater is naturally acidic because carbon ____________ dissolves in it.
10 A chemical compound that forms part of a rock.
11 Remains of plants or animals sometimes found in rocks.
12 This kind of weathering is caused by changes in temperature.
Down
1 Bits of rock are____________ , or carried along, by moving water.
3 Rocks ____________ , or get bigger, when they are heated.
4 The small pieces that make up a rock are called ____________ .
5 Bits of rock are ____________ when water carrying them slows down.
6 ____________ rocks can absorb water.
7 This kind of weathering is caused by acidic rainwater.
9 Sediment often forms ____________when it falls to the sea bed.
Rearrange the letters in the shaded boxes to make a word. _______________________
Write your own clue for this word __________________________________________________
8Ge4 The Dead Sea
Rainwater is not salty. Rain is formed when water evaporates from seas, rivers and lakes, and then condenses again. When the water flows through cracks in rocks it dissolves some chemicals from the rocks. These salts get carried to the sea - this is why sea water is salty.
The Dead Sea is not really a sea at all. It is a lake on the borders of Israel and Jordan. Water flows into the lake from the River Jordan and the surrounding land. The lake is lower than the Mediterranean Sea, which is the nearest sea, and there is no river taking water from the Dead Sea into the Mediterranean Sea. The weather is very hot, with summer temperatures often greater than 40 ºC. A lot of water evaporates from the lake, leaving the salt behind. The Dead Sea is seven times saltier than normal sea water.
The Dead Sea got its name because people thought that nothing could live in such salty water. However, there are a few species of micro-organisms that can live in these conditions.
1 Where does the water come from that falls as rain?
2 Why isn't rainwater salty?
3 How does salt get into the water?
4 Lakes in the UK are not salty. Why do you think this is?
5 Why is the Dead Sea so salty? (Hint: There are two reasons.)
6 The Dead Sea is an interesting place to go swimming. Find out what would be different about swimming in the Dead Sea, and why this happens. (Hint: It would taste saltier, but that is not the answer needed here!)
8Ge5 Evidence from the rocks
We can find out what the landscape and climate were like millions of years ago using evidence from rocks and fossils. Geologists know that some kinds of rock are only formed under water, some are formed in swamps or in river deltas (where the river slows down as it enters the sea, and drops the mud and sand that it is carrying), and so on.
Fact file
- Coral only lives in warm waters.
- Coal is formed when trees and other plants are buried under sediments. This often happens when swamps are flooded.
- The shells found in one layer of mudstone are from animals that only live in the sea.
- Rocks formed from ancient sand dunes have sets of curved layers in them, called cross-bedding, formed as the wind changed the shape of the dunes.
- Coal often contains fossils of plants that would have grown in tropical climates.
- Shale forms when mudstone is squashed.
- Crinoids are sometimes called sea lilies. They lived in clear, shallow water.
- Mudstone can be formed in river deltas or under the sea.
This diagram shows the sequence of rocks found at Stanston in the UK.
1 Which is the oldest rock here: the sandstone or the shale? Explain your answer.
2 Which layer (or layers) of rock formed beneath the sea? Explain your answer.
3 Which layer (or layers) of rock formed from sediments deposited on land? Explain your answer.
4 a Which layers can tell us about the climate when the rocks were forming?
b What was the climate like for each of those layers?
5 Why do you think the layers of rock are different thicknesses? Give as many reasons as you can.
6 Describe what could have happened at Stanston over millions of years to form the sequence of rocks shown.
8Ge6 Dating rocks
Many geologists are interested in finding out what happened to the Earth millions of years ago. They can examine rocks to work out how they were formed, and this can help them to find out if a particular piece of land was once under the sea, or had a river flowing across it.
To get a picture of what was happening to the Earth as a whole (rather than just studying small areas), geologists need to compare what was happening in different places at the same time. To do this, they need to have some way of comparing the ages of rocks in different places. Fossils are very useful in dating rocks.
Living creatures do not stay the same. They evolve over millions of years and form different species. For instance, trilobites were a kind of animal very common around 500 million years ago. If a layer of rock in the UK contains a particular kind of trilobite, geologists can be fairly sure that it is about the same age as rocks with the same kind of trilobite found in Germany, or in the USA.
Different trilobite species.
If geologists are going to use fossils to date rocks, they have to learn about the different species, and how to tell the difference between them. Geologists have worked out when these species of trilobites lived: Trinucleus and Angelina lived between 500 and 430 million years ago, Kettneraspis and Calymene lived between 430 and 395 million years ago, and Paradoxides lived between 570 and 500 million years ago.
1 Why do geologists need to find out how rocks were formed?
2 a Why do they need to compare the ages of rocks from different places?
b How do fossils help them to do this?
3 Look at the drawings of trilobites. If geologists were going to use these trilobites to date layers of rock, they would need to be able to tell them apart.
a Make a table to compare the five trilobites. The headings in your table should include the name of each species, and descriptions of each part of its body.
b Draw a branching key to help someone to identify the trilobites. (Hint: Your first question could be 'Head the same length as body?')
Trilobites have been found in layers A, B and C in this cliff.
a Which species do you think were found in layers A, B and C?
b Explain your answer to part a.
c What can you say about the age of layer D? Explain your answer.
5 The most famous fossils are probably the dinosaurs.
a Find out when the dinosaurs lived.
b Find out why scientists think that the dinosaurs became extinct (died out).
8G Summary Sheets
Rocks and weathering
Rock textures
Rocks are made of grains. Each grain is made of a chemical called a mineral. The texture of a rock depends on the size and shape of the grains.
Sandstone has rounded grains. Sandstone is porous, because water can get into gaps between the grains.
Granite has interlocking grains. The interlocking grains are sometimes called crystals. Rocks with interlocking grains are not porous.
Weathering
Rocks can be worn away by water or by changes in temperature.
Chemical weathering happens when rainwater reacts with minerals in the rock. Rainwater is slightly acidic, because it contains dissolved gases.
Physical weathering can happen in different ways. The minerals in a rock expand if it gets hot, and contract if it cools. These changes in size can produce strong forces. If the rock is heated and cooled over and over again the forces can make cracks in the rock.
Physical weathering can also happen if water gets into a crack in the rock and freezes. Water expands when it turns into ice, and makes the crack wider. This kind of physical weathering is called freeze-thaw action.
Biological weathering is when rocks are broken up or worn away by plants and animals. For example, plant roots can grow into cracks in rocks and make the cracks bigger.
Erosion and transport
Weathered pieces of rock fall to the bottom of cliffs. This movement of bits of rock is called erosion. The bits of rock can be transported away by streams and rivers. Pieces of rock bump into each other while they are being transported, and bits get knocked off them. This is called abrasion. The bits of rock carried by a river are called sediment.
Fast moving water can move larger pieces of rock than slow moving water. Rivers slow down when they flow into a lake or the sea. The slow moving water cannot carry all of the sediment, so some of it is deposited on the bottom. Sediments often form layers. Layers of sediment can also form when sea water evaporates and leaves salts behind.
Sometimes dead plants or animals fall to the bottom of the sea. If their remains get covered by other sediments they may form fossils. When a dead organism forms a fossil, its form can still be seen because either it has not rotted away or its hard parts have been turned into stone. Fossils can help geologists find out how rocks were formed.
If a lot of plant material is buried at once, it may turn into coal. When tiny sea plants and animals get buried they sometimes turn into oil or natural gas. These are all fossil fuels.
8G Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
8Ga
Know what rocks are made of.
Know what texture means.
Know the two main types of rock texture.
Know why some rocks are porous.
8Gb
Know what weathering means.
Know why rainwater causes weathering.
Know what happens to limestone when it is weathered.
Know what happens to granite when it is weathered.
8Gc
Know how temperature changes can weather rock.
Know how freeze-thaw action can weather rock.
Be able to describe conditions when freeze-thaw action will occur.
Understand the difference between chemical and physical weathering.
8Gd
Know what sediment is.
Know about the transport of grains by moving water.
Know what happens to pieces of rock when they are transported.
Know why sediment is deposited.
8Ge
Know why sediment sometimes forms layers.
Know how layers can form from salty water.
Know what fossils are.
Know what coal, oil and natural gas are made from.
8G Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
8Ga - Rock on
Word
Pronunciation
Meaning
crystals
kris-tals
Pieces of a mineral with sharp edges.
grain
Tiny, rounded piece of rock.
interlocking
When crystals fit together with no gaps between them.
minerals
The chemicals that rocks are made from.
mixture
Two or more different kinds of mineral that are not chemically joined to each other.
porous
poor-us
Porous rocks can soak up water.
texture
The scientific word used to describe the shapes and sizes of the crystals or grains in a rock.
8Gb - Out in all weathers
chemical weathering
When rocks are broken up or worn away by chemical reactions, usually with rainwater.
weathered
Rocks that have been worn away or broken up by chemical, biological or physical processes.
8Gc - Hot and cold
biological weathering
When rocks are worn away or broken up due to the activities of living things. For example, growing plant roots can split rocks apart.
contract
Get smaller.
erosion
eh-rO-shun
The movement of loose and weathered rock.
expand
Get bigger.
freeze-thaw action
A type of physical weathering that happens when water gets into a crack in a rock and freezes. The freezing water expands and makes the crack bigger.
physical change
fizz-ick-al
A change that does not involve new chemicals. Melting and freezing are examples of physical changes.
physical weathering
When rocks are worn away or broken up by physical processes such as changes in temperature.
8Gd - Go with the flow
abrasion
When rock fragments bump into each other and wear away.
deposits
When moving water drops rock fragments or grains.
sediment
Rock grains and fragments dropped on the bottom of a river, lake or sea.
transport
The movement of rock grains and fragments by wind or water.
8Ge - Settling down
coal
A fossil fuel made from the remains of plants.
fossils
Any sign of past life that has been preserved in a rock.
natural gas
Fossil fuel formed from the remains of dead plants and animals that lived in the sea.
oil
salts
Chemicals from rocks that have dissolved in water.