L.O: SWBAT what seafloor spreading is & how it helps proves the theory of continental drift.

Pop Quiz: Explain the theory of continental drift the theory of continental drift: all the Earth’s continents were one single giant continent called Pangaea, which broke apart over time and drifted to today’s positions. most scientists didn’t accept Wegener’s theory, because he couldn’t explain why the continent’s drifted.

In the 1960’s scientists discovered the WHY continental drift happens, when they used sonar to map the ocean floor!

What did they find? The sea floor is spreading. Oceans are getting wider therefore pushing the continents apart.

What do you see happening here? As the NEW seafloor hardens, the OLD seafloor is pushed away this is called seafloor spreading. What do you see happening here?

*seafloor spreading: the pushing away of old seafloor as new oceanic crust is formed at mid-ocean ridges . the newer & younger seafloor makes the ocean floor wider, as it pushes away the older seafloor L.O: SWBAT: what seafloor spreading is.

Seafloor spreading is the cause of continental drift *Seafloor spreading is the cause of continental drift! As the seafloor spreads, it pushes the continents away from each other! L.O: SWBAT: what seafloor spreading is.

The mid ocean ridges (underwater mountain ranges) are where the seafloor spreading happens. L.O: SWBAT: what seafloor spreading is.

Proof of seafloor spreading…. The Age of oceanic basalt rocks. 2.Magnetic measurements of oceanic rocks. L.O: SWBAT: what seafloor spreading is.

1. Age of the oceanic bedrock suggests new sea floor is being created. a) Youngest rock at mid-ocean ridge where new sea floor is created. b) Oldest rock is found near continents where old sea floor is subducted (goes underneath) where it melts and is recycled. c) Rocks equidistant from the mid- ocean ridge in opposite directions are of the same age.

The rocks at location A and E are the oldest The rocks at location A and E are the oldest. The rocks at B and D are of the same age because they are equidistant from the ridge in opposite directions. Place an “X” where the youngest rocks are located.   Draw arrows from the X pointing towards the older rocks. x

As the distance away from the mid-ocean ridge increases the age of the rocks (oceanic crust) increases.

In the south In the north Where is the north pole located? Where is the south pole located? In the south L.O: SWBAT: what seafloor spreading is.

10,000 years ago, the North pole was south and the South Pole was north! The Earth is a giant magnet. Every 10,000 years, the magnetic poles flip and reverse. How do we know? L.O: SWBAT: what seafloor spreading is.

The normal and reversed matching patterns magnetism on both sides of a mid-ocean ridge is a proof of seafloor spreading! Copy at the bottom of your notes: When molten rock hardens, the minerals align with the Earth’s magnetic field. forming a permanent record of what the earth’s magnetic field was like at the time. L.O: SWBAT: what seafloor spreading is.