Transcript Earth*s Changes

Earth’s Features
• ¾ of Earth is covered by water.
–Most of the water is in oceans.
• Earth has 7 great areas of land
called continents.
–North America (where we live)
Landforms
• Mountain – tallest; has steep sides and pointed
top
• Valley – low land between hills or mountains.
• Canyon – deep valley with steep sides
• Plain – land that is wide and flat
• Plateau – steep sides and a flat top; higher than
land around it.
• Coast - land that borders the ocean
• Peninsula – land surrounded by water on 3 sides
• Island – land with water all around it
Water Features
• Ocean – large bodies of salt water
• Lake – water that is surrounded by
land; can be fresh or salt water
• River – large body of moving fresh
water
• Glacier – a large, slow moving, block
of ice
Land Features in the Ocean
• Ocean Floor – Land below the ocean.
• Continental Shelf – a huge plateau
that lies under the ocean at the edge
of a continent.
• Abyssal Plain – wide and flat, stretches
thousands of kilometers across the
ocean.
• Trench – a canyon on the ocean floor.
Layers of the Earth
• Crust – The outermost layer
– Made up of the continents and the ocean floor
– The thinnest and coolest layer
• Mantle – Layer below the crust
– Part solid rock
– Part nearly melted rock that is soft and flows (like putty)
• Core – Deepest and hottest layer of Earth
– Outer Core – Melted Rock
– Inner Core – Solid Rock
Sudden
Changes to
Earth
Earthquakes
• A sudden movement of the rocks
that make up the Earth’s crust
• The ground shakes or vibrates.
• Some earthquakes are very weak and
aren’t even noticed while others are
very strong.
–Some can crack roads or even
cause mountains to fall!
Volcanoes
• A mountain that builds up around an
opening in Earth’s crust
–Melted rock (magma) moves through a
large crack in the crust and flows onto land.
–When it flows onto land it is called lava.
–If the lava is forced out in an explosion a
large part of the mountains is blown away
• Materials from volcanoes can cause a lot of
damage to buildings and living things.
Landslides
• The rapid movement of rocks and
soil down a hill.
• Caused by gravity.
• Can change a hill or mountain very
quickly.
Floods
• Water that flows over land that is
usually dry.
• Can be caused by heavy rains and
melting snow.
• Flood waters are very strong.
Weathering,
Erosion, and
Deposition
What is Weathering?
• The breaking down of rocks
into smaller pieces is called
weathering.
• Happens so slowly you cannot
see it.
• Can take millions of years.
What causes weathering?
• Running water and Wind
– Pick up small rocks that scrape against other
rocks
– The scraping slowly wears away rocks.
• Rain and Melting Snow
– Enter cracks in rocks
– Water freezes and expands widening the crack before
thawing and becoming liquid again
– Over time, repeated freezing and thawing breaks rocks
apart.
What causes weathering?
• Living Things
–Plants grow in the cracks of rocks
• The roots eventually split rocks apart
–Animals dig in the ground
• They uncover buried rocks
• The uncovered rocks can then begin
to weather.
What is Erosion?
• The movement of weathered rock
• Moving water, wind, and glaciers
and gravity all cause erosion
• Happens very slowly
• Weathering and erosion work
together to change the land
Moving Water and Wind
• Moving water and wind picks up
rocks and sand
• The rocks and sand may be carried
far away and dropped in new
places.
• Deposition – the dropping off of
weathered rock.
Glaciers
• While moving a glacier picks up and
carries rocks of all sizes.
• The ice at the bottom of the glacier
freezes onto rocks and tears them out
of the ground
• Can move rocks the size of a house.
• As glacier melts, rocks are dropped
off in a new place.
People change the Land
• Small Changes
–Digging a hole in your backyard
• Large Changes
–Trees cut down to build roads, stores, and
homes
• If trees are not replanted, soil can wash away
–Ponds and swamps are drained
• Dry soil left behind can blow away
–Land is dug up to reach valuable rocks