in appearance. Many metals are quite
hard. Metals can be stretched into wire
or rolled into sheets. Many metals conduct,
or carry, electricity well.
Where Metals Are Found
Living things have certain metals within
some of their cells. But the metals that
people use to make things are found in
Earth’s crust. Only gold and a few other
metals can be found in pure form. Most
metals are always found in the form of
chemical compounds. (Chemical compounds
are mixtures of two or more
Ancient
peoples used
the metals
bronze and
iron to make
tools and
weapons.
An illustration shows Metacom,
who led the Wampanoag
against settlers in King Philip’s
War. It was one of the deadliest
wars between settlers and Native
Americans.
BRITANNICA STUDENT ENCYCLOPEDIA Metal 105
chemical elements.) A rock that contains
a metallic chemical compound is called
an ore.
Extracting Metals
Metallurgy is the science of separating
metals from ore and then working with
the metals. The first step in producing a
metal is to crush the ore into small
pieces. The next step is to purify, or
clean, the ore.
Metallurgists then take apart the
chemical compound that contains the
metal. Sometimes they heat the ore so
that the chemical elements separate and
liquid metal flows out. This process is
called smelting. Metallurgists also use
electricity and chemicals to separate
metal from ore.
Workers then shape the metal. They
may shape it by pouring it into a mold,
hammering it on a hard surface, rolling
it into sheets, or forcing it through
openings.
Alloys
Metallurgists sometimes melt metals and
mix them together with other metals or
with nonmetals. This produces new
metals called alloys. Steel is an alloy of
iron and carbon. Bronze is an alloy of
copper and tin. An alloy has different
characteristics than a metal alone. It may
be stronger or stand up better to heat.
History
Gold and copper were the first metals to
be discovered. Then came silver, lead,
tin, iron, and mercury. At first, people
simply hammered metals into shape.
Then they learned to melt metals and
The metal in a garden chair has
been shaped into flower designs.
Metals are solid and very strong
at room temperature. But when
heated, metals become liquid.
This makes it easy to form them
into different shapes.
Giant conveyor belts carry ore,
or rock containing metal, that
has been dug from the ground.
The metal must be separated
from the ore before it can be used.
106 Metal BRITANNICA STUDENT ENCYCLOPEDIA
pour them into molds. More than 5,000
years ago, people made the first alloy—
bronze. More than 3,000 years ago,
people learned to purify iron, which is
stronger than bronze.
During the Middle Ages (AD 500–1500)
people tried to change lead and other
metals into gold. They did not succeed,
but they found out many things about
metals. Modern scientists have discovered
many new metals and have learned
to use metals in many new ways.
#More to explore
Alloy • Bronze • Chemical Element
• Iron
Metamorphosis
Metamorphosis is a process some animals
go through to become adults. It is a
series of physical changes. Metamorphosis
is especially common in insects.
Genes and chemicals called hormones
control the process.
Many insects go through four stages of
metamorphosis: egg, larva, pupa, and
adult. An insect hatches from an egg
into a wormlike larva. Caterpillars are
examples of insect larvae. The larva eats
a lot. As it grows, the larva molts, or
sheds its outer covering. To begin the
pupa stage, the larva often builds a protective
covering, such as a cocoon. Inside
this covering the pupa develops wings
and adult body parts. It comes out of its
covering as an adult.
Beetles, butterflies, flies, and wasps are
among the insects with four stages of
metamorphosis. Some insects, such as
grasshoppers and termites, have fewer
stages.
Through metamorphosis, a frog develops
from an egg to a tadpole and then to an
adult.
BRITANNICA STUDENT ENCYCLOPEDIA Metamorphosis 107
Metamorphosis also happens in animals
other than insects. Most amphibians go
through metamorphosis. For example, a
frog begins life as a tadpole. A tadpole
has a short, oval body with a tail. It
gradually develops legs and loses its tail
to become an adult frog. Starfish, crabs,
lobsters, snails, and clams also go
through metamorphosis.
#More to explore
Amphibian • Butterfly and Moth
• Hormone • Insect
Meteor and
Meteorite
A meteoroid is a chunk of rock or metal
from space that falls through the atmosphere,
or layer of gases, surrounding
Earth. Most meteoroids burn up in the
atmosphere. This creates a bright streak
of light called a meteor. Meteors are also
called shooting stars. If a meteoroid survives
its fall and reaches Earth’s surface,
it is called a meteorite.
Almost all meteoroids are formed from
material that breaks off objects in space
called comets or asteroids. The chunk of
rock or metal may enter Earth’s atmosphere
traveling as fast as 45 miles (72
kilometers) per second. Most meteoroids
melt from the heat or break up from the
pressure within seconds.
At times people can see thousands of
meteors per hour. These meteor showers
often occur as Earth passes through the
