Download Alfred Wegener was a scientist who lived about 100 years ago

Plate Tectonics
Alfred Wegener was a scientist who lived about 100 years ago. His idea was that the
continents had drifted apart. He found evidence to support his idea such as:
The shapes of the continents appear to fit together like pieces of a puzzle.
The fossils and rocks along the edges of continent match those on other continents.
The people in his time did not accept this idea because he couldn’t explain how
continents could move.
After Alfred Wegener died, new technologies were invented that led to new discoveries
which led to the modern theory of plate tectonics. One new technology, sonar, allowed
scientists to make a map of the ocean floor. Scientists discovered a long, underwater
system of cracks on the sea-floor called mid-ocean ridges. Another new technology
called radioactive dating allowed scientists to measure the age of rocks. They discovered
that the sea floor near mid-ocean ridges is very young while rocks farther away are much
older. These discoveries led to the idea that the sea floor is spreading apart at mid-ocean
ridges (sea-floor spreading).
The theory of plate tectonics says that the Earth’s crust is broken into pieces called
tectonic plates. There is evidence to suggest that the tectonic plates move around due to
convection currents in the mantle below. The energy that drives the convection comes
from the heat in the core of the earth. Where plates split apart at mid-ocean ridges, molten
material rises to fill in the gap. The older edges of plates are subducted back into the
mantle at trenches.
Earthquakes are most common at the boundaries, or edges, of the tectonic plates where
the plates are converging (coming together), diverging (moving apart), or sliding against
each other side by side (transform). In fact, scientists have located the boundaries of
tectonic plates by mapping the location of earthquakes all over the world. Volcanoes
occur near plate boundaries if one plate is subducting beneath another plate. Where two
continents converge, mountains are pushed up. Where an ocean plate converges with a
continent, the ocean floor subducts beneath the continent, creating volcanoes on the
continent. Where two ocean plates converge, the plate which is more dense subducts,
creating volcanic islands on the upper plate.
Moving tectonic plates can have major effects on earth’s other systems. Continents
sitting on moving plates can drift to different parts of the earth, causing the climate of
that continent to change. This also affects what kinds of living organisms can live on that
continent. Drifting continents can also change the path of ocean currents and wind
currents. Subducting plates can cause volcanic eruptions large enough to send ash high
into the air. The ash can circle the earth, blocking out sunlight and causing the earth to
cool. Moving plates can push up mountains that can block winds and change weather
patterns. The movement of earth’s crust has huge effects on earth’s other systems.