Page 17 - Exercise 1A

Page 17 - Exercise 1A

The first materials that people used were stone, wood and bones, but around 4000 BC die first metal tools appeared.

They were made of copper. In fact, people had metal before that time. They already knew about gold and silver, but these were too soft for tools. Copper, however, is hard enough and copper tools were much sharper than stone tools. W e don’t know how people discovered copper. It was probably when they put some rocks round a fire and die fiie melted the metal in die rocks.

Soon people discovered that if you mix copper with a little tin, you get an even stronger material. We call this bronze. With their new tools, Bronze Age people could do many more things. In particular, they could cut rocks to build houses, palaces, temples and huge monuments, like the Pyramids. However, there was a problem. Although copper was quite common, tin was not, so bronze was always expensive. Then, around 1500 BC people discovered a new metal - iron. Iron is a very’ common mineral. Almost 5% of the Earth’s crust is iron and scientists believe that the red colour of die planet Mars is iron, too. With the Iron Age, tools and weapons became a lot cheaper.

Although iron ore is very common, people needed charcoal to make it into iron. Charcoal is made from wood and by the 18th century, Europe didn’t have enough trees. However, an Englishman, Abraham Darby, discovered how to use coal instead of wood.

Coal was very common and this led to the Industrial Revolution. People used iron and steel, which is made from iron, to build machines, steam engines, bridges, railways and many more things.

Stone, wood and metal are all natural materials. However, in the 19th century, scientists discovered that they could separate the molecules of some materials and make completely new ones.

We call them synthetic materials, or plastic. The first real plastic - Bakelite - appeared in 1909. Over die next thirty years other kinds of plastic. such as PVC, polystyrene and nylon, appeared. Chemists are still producing new kinds of plastic today.