In the 17th, 18th and 19th centuries, new countries were being discovered and explored. James Cook's voyages took him to Australia and the Antarctic. John Franklin headed north to the Arctic Circle in search of the North West Passage.

You can download larger versions of the 'Death of Captain Cook' and Cook's letter to the Royal Society here.

The Great Barrier Reef

You will need...

Two glasses of water
Red cabbage indicator ( see instructions here)
A straw
A plastic beaker
Some eggshell

How long will it take?

It only takes about 15 minutes to carry out these little experiments, but you may want to leave the eggshell for a while longer to see the effect of the acid over a longer period of time.

What to do...

1.  You will need to make up some red cabbage indicator (or use a pre-prepared indicator if you would prefer).  Red cabbage indicator is made by boiling red cabbage in water for a few minutes.  Strain the water into a jug, and let it cool.  This indicator will change to a range of colours in different acids and alkalis.

2.  Read the instructions in the students' section.

3.  The students can work in small groups or individually, but you may want them to compare their results.

4.  Once the students have tried changing the colour of the indicator by blowing carbon dioxide into the glass of water, you may like to get them to try it for different times, e.g. 15 seconds, 30 seconds, etc. to see if there is a noticeable difference in the acidity of the water.

5.  The students should see the red cabbage indicator turning from a blue colour to a purple / pink colour as the indicator reacts with the acid in the water. 

6.  The egg shells will start to dissolve in the vinegar.  The vinegar is a much stronger acid than the carbon dioxide dissolved in water, so it shows a speeded up reaction of what is happening to the shells of sea creatures in an increasingly acidified ocean.


Curriculum Links


Working Scientifically


Animals including humans


Lower key stage 2 Year 4
Living things and their habitats


Upper key stage 2 Year 5
Properties and changes of materials


Upper key stage 2 Year 6
Living things and their habitats


Geographical skills and fieldwork


A study of an aspect or theme in British history that extends pupils' chronological knowledge beyond 1066


Scottish Curriculum



SCN 2-01a

Planet Earth - Biodiversity and interdependence.


SCN 2-15a

Materials - Properties and uses of substances

Social Studies


SOC 2-01a

People, past events and societies.

Using primary and secondary sources selectively to research events in the past.


SOC 2-04a

People, past events and societies

Comparing and contrasting a society in the past with my own and contributing to a discussion on the similarities and differences.


SOC 2-06a

People, past events and societies

Discussing why people and events from a particular time in the past were important, placing them within a historical sequence.


SOC 2-08a

People, past events and societies

Discussing the environmental impact of human activity and suggesting ways in which we can live in a more environmentally-responsible way.

James Cook and the South Pole

James Cook was a captain in the Royal Navy.  He is famous for exploring the Pacific Ocean, where he made maps of New Zealand and Hawaii and explored the Great Barrier Reef.  In 1773 he sailed closer to the Antarctic than anyone had before. 

cook letterJames Cook made three voyages.  The first was paid for by the Royal Society so scientists could observe the transit of Venus: where Venus is seen as a dot moving in front of the Sun.  Also on board was Joseph Banks, who picked up many new plants to bring back to England.

This second voyage was to find the large continent known at the time as Terra Australis, south of Australia.  In the end he did not find the Antarctic but came very close.   During his second trip, Cook managed to prevent the disease called scurvy from killing any of the sailors on his ship (on a long voyage up to two thirds of the sailors could die of scurvy!)  It may have been the fresh food that Cook picked up, or the 'malt' he gave them, but it showed that nutrition was linked to the prevention of some diseases  (look at the Trailblazing entry for 1776). 

Have a look at the letter that James Cook wrote to the Royal Society on his return from his second voyage.   Can you find out why he is writing the letter and what James Cook thought gave his men an 'uncommon good state of health'? Click here to read a typed version of the letter.

death cookCook's third voyage took him south into the Pacific, then north where he mapped up the west coast of America, and he then searched for a way through the Arctic back to the Atlantic Ocean, a route known as the North West Passage.  The ship could not make it through, and when it returned to Hawaii Cook was killed and cooked by the Hawaiians!






The Great Barrier Reef

coral polypOn Cook's first voyage his ship became stuck on the Great Barrier Reef.  The reef is not made of rocks, but of coral, and it is the biggest natural object visible from space.

Coral polyps are tiny jellyfish-like creatures that produce a hard skeleton made of calcium carbonate, the same material as eggshells.  Although coral is clear, tiny coloured algae live inside the coral and give the coral its colour.  The algae uses sunlight to make its food just like plants on land, and the coral polyps eat some of the algae. 


You will need...

Two glasses of water
Red cabbage indicator ( see instructions here)
A straw
A plastic beaker
Some eggshell

What to do...

Part 1

Cabbage indicator_3001.  Add some of the red cabbage indicator to one of the glasses of water - have a look at the colour.

2.  Add indicator to the second glass of water.

3.  Blow through a straw into the second glass of water and compare the colour with the first glass (don't suck the water up!).

Part 2

1.  Pop the eggshell in the plastic beaker.

2.  Add some vinegar.

3.  Watch as it bubbles away.

4.  Leave it for a couple of days, and observe what happens.


What is happening?

When you blow out into the water in part 1, you are adding carbon dioxide to the water (because we breathe in oxygen and blow out more carbon dioxide).  A small part of the carbon dioxide dissolves in the water, just like sugar or salt dissolves in water.  The carbon dioxide in the water makes carbonic acid: it is very dilute but it makes the water acidic.   

Carbon dioxide from the air is dissolving in the sea in the same way, and is slowly making the ocean more acidic.

The shells of many sea animals are made of calcium carbonate, and they react with this acid in the sea in much the same way as the eggshells react to the vinegar in part 2, although the reaction is much slower.

Coral reefs are also affected by the increasing sea temperature due to climate change.  They react by getting rid of the algae which lives in the coral.  This is called coral bleaching as the coral returns to its original white colour.  The loss of algae starves the coral and the reef dies. 

The combination of warmer waters and increased acid is making it harder for the coral reefs to survive.