5th Science (Thin Book)

The following notes are for those 5th graders who are working out the McDougal Littell "thin" textbook.  Refer to pages 14-19.

Continents change position over time.

Vocabulary:

• Continental Drift:
  • Definition:  the hypothesis that earth's continents move on earth's surface
  • Sentence:  Evidence, such as fossils, climate, and geology, support continental drift
  • Characteristics:  the hypothesis that earth's continents move on earth's surface:  Scientist did not take continental drift seriously until the mid-1900s we new evidence was founded.

• Pangea:
  • Definition:  a hypothetical supercontinent that included all of the landmasses on earth 
  • Sentence:  180 million years ago Pangea spilt into Gondwana and Laurasia.
  • Characteristics: The supercontinent began breaking apart about 200 million years ago.

• Mid-Ocean Ridge:
  • Definition:  a long line of sea-floor mountains where  new ocean crust is formed by volcanic activity along a divergent boundary
  • Sentence:  Mid-ocean ridges appear in every ocean, circling earth like seams in a baseball.
  • Characteristics:  Scientists began mapping the sea floor in detail in the 1950s.

• Convection:
  • Definition:  the transfer of energy from place to place by the motion of heated gas or liquid; in earth's mantle. convection is thought to transfer energy by the motion of soild rock, which when under great heat & pressure can move like a liquid
  • Sentence:  Convection takes place when you boil a pot of water.  The water at the bottom of the pot heats up, becomes less dense, and rises.  At the surface, it cools, becomes denser, and sinks, only to be heated and rise again.
  • Characteristics:  Rock in the the asthenosphere and mantle move by convection.

• Convection Currents:
  • Definition:  A circulation patteren in which material is heated and rises in one area, then cools and sinks in another area, following in a continous loop.
  • Sentence:  Convection current is a motion that transfers heat in a material.
  • Characteristics:  The movement of rock in the mantle is an example of convection currents.

• Theory of Plate Tectonics:
  • Definition:  A theory stating that Earth's lithosphere is broken into huge plates that move and change in size over time.
  • Sentence:  As scientist studied the plates they found that plates can move apart, push together, or scrape past each other.
  • Characteristics:  Major Plates: the African Plate, the Antarctic Plate, the Australin Plate, the Indian Plate, the Earasian Plate, the Nazca Plate, The North American Plate, and the Pacific Plate

Continents join togeter and  spilt apart. (page 14)

Time Period	Events Supporting Continental Drift
1500's	mapmakers noticed the western coast of Africa and the eastern coast of South America seemed to fit together
1800's	Alfred Wegner, German scientist, began studying how contintents seemed to fit together.
1912	Wegner proposed a hypothesis known as continental drift. Wegner tought that earth's continnents were once joined in a single landmass & gradually difted apart. For many years people did not accept Wegner's ideas.
Mid-1900's	New evidence supports Wegner's ideas.

Evidence from the Sea Floor (pages 16-17):
·         1950’s:  scientist began mapping the sea floor
o   they expected to find a smooth & level floor
o   they found mountain ranges called mid-ocean ridges

Evidence	Details
Sea-Floor Spreading	·         melted rock; o    rises through the cracks o   cools o   forms new oceanic crust ·         spreading centers o   old crust is pulled away to make room for new material o   the sea floor slowly spreads apart
Age of the Sea Floor	o   rock samples show; o    youngest rock is closest to the ridge o   oldest rock is farthest away o   oldest ocean floor is 160 to 180 million years old o   continental crust is up to 4 billion years old o   the ocean floor is always forming & moving o   sea floor moves = tectonic plates & continents move
Ocean Trenches	o   old crust is being destroyed at the same rate that new crust is forming o   dense oceanic crust is sinking into the huge trenches in the sea floor & then into the asthenosphere

 
Causes of Plate Movement (pages 17-18):
o   asthenosphere:
o   a layer of soft, hot rock
o   where tectonic plates rest
o   rock in this layer, along with the mantle, move by convection
o   Convection:
o   heat transferred by the movement of a material
o   example: when boiling water the water
§   at the bottom heats up
§   becomes less dense
§   rises
§  cools at the surface
§  becomes less denser
§  sinks
§  heated & rises again
o   Convection Current:
o   continuous motion that transfers heat in a material
o   the rock in the astenosphere acts like boiling water
§  the hot, soft rock rises, cools, & sinks
§  it is heated & rises again
o   occurs slowly
o   moves tectonic plates
o   slap pull & ridge push:
o   also move plates
o   slap pull occurs where gravity pull the edge of a cool, dense plate into the asthenosphere
o   ridge push occurs when material from a mid-ocean ridge slides downhill from the ridge
Putting the Theory Together (pages 18-19):
·         The theory of plate tectonics:  Earth’s lithosphere is made up of huge plates that move over the surface of the Earth

updates 11/26 at 2:50 pm