Transcript Plates - cloudfront.net

Plates: History and
Evidence
Earth Science Standard 3a and b
History
• 1912: German
Alfred Wegener:
continents fit like a
puzzle.
• Called continental
drift.
• Many doubted him!
Supercontinent 250 mya
• Called Pangaea by Wegener in 1928.
• Ocean around it called Panthalassa.
• Broke apart over time.
• Ignored due to lack of evidence until
1960’s
• Convection was discovered  plates
move due to heat rising from mantle.
Evidence for Plates:
Example 1, The
Cynognathus
South America
Africa
• 1) Far away continents have similar fossils
and rocks of the same age.
• Determined by radioactive dating.
Evidence for Plates:
Example 2: Rock Age
at Mid Ocean Ridges
Mid-Ocean
Ridges: Place
where plates
pull apart
new crust
made
How?? Plates must be moving if same age on
both sides!
Rock A: 65 my old
Rock B: 65 my old
Evidence for Plates: Example 3:
Magnetism at Mid Ocean Ridges
• Mantle comes up and cools to form rocks.
• Rocks (with Iron in them) align to earth’s
magnetic field Permanently hardens
• Creates banded patterns
Evidence for Plates
Scientists collected these rock samples
from the bottom of the ocean. Turn
to your partner and discuss whether
or not you would ever want to
journey down to the bottom of the
ocean. Why/why not?
Question! The drawing below shows
magnetic patterns in oceanrust on either
side of a mid-ocean ridge. The ocean crust
at Point 1 is 60 million years old. What is
most likely the age of the crust at Point 2?