Page 21 - cosmos4
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Babies have about 300 bones at birth, with cartilage between
many of them.
When a substance is heated up, its particles move
more and it takes up a larger volume – this is known as thermal
expansion. For this reason, large structures such as bridges are built with
expansion joints which allow them some leeway to expand and contract without
causing any damage.
Our atmosphere is made up of roughly 78 per cent nitrogen and 21 per cent oxygen,
with various other gases present in small amounts. Covering 5.5 million square
kilometres (2.1 million square miles), the Amazon rainforest cycles a significant
proportion of the Earth’s oxygen, absorbing large quantities of carbon dioxide at the
same time.
There are certain metals – including potassium, sodium, lithium, rubidium and
caesium – that are so reactive that they oxidize (or tarnish) instantly when exposed
to air. They can even produce explosions when dropped in water!
A neutron star is the remnants of a massive star that has run out of fuel. Typical
neutron stars have a mass of up to three solar masses, which is crammed into a
sphere with a radius of approximately ten kilometres (6.2 miles) – resulting in some
of the densest matter in the known universe.
