Page 22 - cosmos4

The Earth’s crust is split into gigantic pieces called tectonic plates. These plates are
in constant motion, propelled by currents in the Earth’s upper mantle. Hawaii sits in
the middle of the Pacific Plate, which is slowly drifting north-west towards the North
American Plate, back to Alaska. The plates’ pace is comparable to the speed at
which our fingernails grow.

Tiny single-celled algae called coccolithophores have lived in Earth’s oceans for 200
million years. Unlike any other marine plant, they surround themselves with
minuscule plates of calcite. As further sediment built up on top, the pressure
compressed the coccoliths to form rock, creating chalk deposits Carbon dating
estimates a fossil’s age more precisely, based on the rate of decay of radioactive
elements such as carbon-14.

Over the coming hundreds of millions of years, the Sun will continue to get
progressively brighter and hotter. In just over 2 billion years, temperatures will be
high enough to evaporate our oceans, making life on Earth impossible.

Thermal cameras detect the heat lost by a subject as infrared, but polar bears are
experts at conserving heat. The bears keep warm due to a thick layer of blubber
under the skin. Add to this a dense fur coat and they can endure the chilliest Arctic
day.

In space, light travels at 300,000 kilometres (186,000 miles) per second. Even at this
breakneck speed, covering the 150 million odd kilometres (93 million miles) between
us and the Sun takes considerable time. And eight minutes is still very little
compared to the five and a half hours it takes for the Sun’s light to reach Pluto.