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The Earth’s Drifting
Continents
Theory of Continental Drift
• Alfred Wegener suggested
that the continents were
once together and have
since drifted apart. Was not
accepted until 30 years later.
Pangea
• The earth had a single
landmass that broke up into
large pieces, which have
since moved apart.
Evidence to Support
Continental Drift
• Fossils- preserved remains of
organisms
• Rock formations and
deposits; coal, limestone,
salt, etc.
Basalt from a volcanic eruption.
Evidence Cont…
• Mountain chains
• Coal fields
• Glacial deposits
The Earth’s Spreading
Ocean Floor
Mid-ocean Ridges
• Under water mountains and
valleys.
Trenches
• V shaped valleys at the
bottom of oceans, which are
usually found on the edges
of continents and islands.
• Deepest part of the ocean
Ocean Floor Spreading
• Lava erupts at rift valleys
and hardens to form new
ocean floor.
• Explains how the continents
move.
Subduction
• Process in which old crust
plunges back into the earth.
• Rocks are pushed deep into
trenches where they are
melted by the heat of the
earth. They recycle.
Evidence to Support Ocean
Floor Spreading
• Rock age- youngest rocks
are found near rift valleys
and oldest rocks are found
near trenches.
Evidence Cont…
• Magnetic Stripesmagnetic rock line up with
the poles equally on both
sides of the mid-ocean
ridge.