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Active PlanetEarth is a dynamic planet that is always changing its form. Heat generated by nuclear reactions deep below the surface creates hugely powerful currents that keep Earths rocks on the move, triggering earthquakes and volcanic eruptions. Meanwhile, solar energy striking the planet in different ways creates currents in the air, driving the atmospheric turmoil of the weather. This changes with the seasons and from place to place, creating an enormous range of climates and habitats for the most dynamic element of alllife.
THE PLATES OF EARTHS CRUSTHeat generated deep within the planet creates currents in the mobile mantle rock beneath the crust. These currents drag some sections of the cool, brittle crust apart while pushing other parts together, fracturing the crust into separate plates. The biggest of these span oceans and continents, but there are many smaller plates. At their boundaries the plates may be diverging (pulling apart), converging (pushing together), or sliding past each other at transform faults.
WHERE MOVING PLATES MEETThe boundaries between the plates are volcanic earthquake zones. The plates move very slowly, pulling apart at divergent boundaries. This allows hot rock below to melt, erupt, and cool to form new crust especially at the spreading rifts that form mid-ocean ridges. Meanwhile, at convergent boundaries, one plate slides beneath another, pushing up mountain ranges and making volcanoes erupt. Other volcanoes erupt over hot spots in the mantle below the crust.
CaribbeanPlate
Cocos Plate
North American Plate North American Plate
Eurasian Plate
African Plate
Antarctic Plate
Indo-AustralianPlate
PacificPlate
PacificPlate South American
Plate
NazcaPlate
Key to map
Divergent boundary
Convergent boundary
Transform fault
Uncertainboundary
Lower atmosphere, 10 miles (16 km) thick
Crust, 545 miles (870 km) thick
Continental crust, much thicker than oceanic crust
Broad basin formed near uplifted area
Ancient converging boundary, now inactive
Mountains created when plate boundary was active
Oceanic crust formed from heavy basalt rock
Upper mantle, mostly solid but very hot
Mantle, solid but mobile owing to heat currents
Spreading rift forming a mid-ocean ridge
Hot-spot volcano erupting over mantle plume
Mantle, 1,800 miles (2,900 km) thick Liquid outer
core, 1,400 miles (2,250 km) thick
Solid inner core, 1,515 miles (2,440 km) across
ACTIVE PLANET
DOWN TO THE COREEarth formed from iron-rich asteroids that
smashed together to build the planet. Early in its history it, melted, allowing
the heavy iron to sink and create a metallic core. The core is
surrounded by lighter rock, with the lightest forming Earths crust. Most of the water on the planet lies in huge oceans, and above
them is the layer of air that forms the atmosphere.
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Ocean trench marking convergent plate boundary
Volcano erupting over convergent boundary
Earthquake zoneone plate grinding under another
Plates pulling apart, creating a rift valley
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(c) 2011 Dorling Kindersley. All Rights Reserved.
ACTIVE PLANET
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Key to map
Less than 20 cm (50 in)
2079 in (50200 cm)
More than 79 in (200 cm)
December is the southern summer and
northern winter
Arctic Circle, where Suns rays
are dispersed
Equator, where Suns rays are
concentrated
March is the northern spring
June is the northern summer and southern winter
Sahara Desert
Atacama Desert, Chile
The Sun
Rising warm, moist air near Equator
Rainforest, Borneo
Tropic of Capricorn
THE SEASONSEarth spins on a tilted axis, so as it orbits the Sun once a
year, the North Pole points toward the Sun in June and away from it in December. This means that in
regions north of the Tropics it is summer in June but winter in Decemberand the opposite is
true to the south of the tropics. Near the Equator it is always warm and there are
annual wet and dry seasons.
COLD POLEThe Tropics are the hottest parts of the planet because the Suns rays directly
strike them, concentrating the heat energy. Near the poles the same amount
of heat energy is spread out over a broader area, so it does not have as much
heating effect, even in the summer. At midwinter, the entire polar region is in
permanent darkness, so it gets no solar energy at all and is bitterly cold.
JUNGLE AND DESERTConcentrated sunlight near the Equator heats Earths surface, warming the air above. The warm air rises, carrying moisture with it. This forms huge clouds that spill tropical rain, fueling the growth of rainforests. The dry, cooling air then flows north and south and sinks over the subtropics, creating deserts. Similar air-circulation patterns affect the climate in the far north and south.
RAINFALLSome parts of the world get much more rain than others.
The wettest regions are mostly rainforest zones, where year-round rain and warmth promote lush plant growth.
Regions of moderate rainfall are naturally forests and grasslands, although most of this land is now used for
farming. The driest regions may be too dry for many plants to grow, creating desertsbut they also include
some northern forest zones and polar tundra.
Descending cool, dry air over desert zone
Cold air (in blue) becomes chilled in upper atmosphere
Warm air (in red) heats up near Earths surface
Cool, dry air sinks over desert zone
Tropic of Cancer
Earths axis
South Pole
North Pole
(c) 2011 Dorling Kindersley. All Rights Reserved.
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