Today  Hand in any work needed.  Check the list in the back, if you owe something.  Get out a small piece of paper, PUT YOUR NAME ON IT.  When bell rings the quiz will start and you will have 1 minute per question to answer.

Question 1  What is the density of the 2 types of crust?

Question 2  Evidence of continents moving (2)?

Question 3  What element is the crust made out of mostly?

Question 4  What is LAT/LONG of Hawaii hot spot?

Answers  What is the density of the 2 types of crust? 3.0=oceanic 2.7=cont 3.0=oceanic 2.7=cont  Evidence of continents moving (2)? Puzzle, fossils, mtns, sea floor spreading Puzzle, fossils, mtns, sea floor spreading  What element is the crust made out of mostly? Oxygen Oxygen  What is LAT/LONG of Hawaii hot spot? 20 o N 160 o W 20 o N 160 o W

Sea Floor Spreading And Other Plate Boundaries

Continental drift  Idea that continents “floated” on the ocean and moved into current locations.  This idea was argued against from its beginning. The ocean floor was thought to be flat The ocean floor was thought to be flat How can the continents move? They are so big?! How can the continents move? They are so big?!  Continents float.  Alfred Wegner Continents float.

Continental Drift

Hess’s Discovery  In the 1950’s a Naval Captain made a discovery.  In the 1950’s a Naval Captain Henry Hess made a discovery.  Hess found that the ocean floor was not flat at all.  Further research proved that it was in fact like a mountain range. DEMO

New idea?  Scientists looked at the continental shelf and saw the pieces fit together much better.  We call this not  We call this Plate Tectonics not Continental Drift  Plate tectonics is the movement of the plates on the mantle!  New technology allowed scientists to see another fact called  New technology allowed scientists to see another fact called paleo- magnetism.

Gabbro verses a compass  What is the composition of gabbro?  So the Iron in it should always be aligned to the polarity of the Earth?  If we put a compass on the rock it will show the rock it will show the magnetic field that was magnetic field that was frozen into the rock when frozen into the rock when it formed. it formed.

How does that explain anything?  If I took water and put iron in it and then froze it the iron would be the same direction. But if I put it in and before I froze it, then switched the field around the ice tray the iron would align and refreeze the opposite way! But if I put it in and before I froze it, then switched the field around the ice tray the iron would align and refreeze the opposite way!  If the fields in the rock have been flipped then this mean the fields on Earth have been flipped!

How does this work?  Convection moves the plates  the empty space creating new rock.  New magma fills the empty space creating new rock.  around Earth at that time.  This new rock saves the magnetic field around Earth at that time.  **Think of a grocery stores check out.**

Paleo-Magnetism   Using the Earth’s recorded magnetic field in rocks to understand the past.   This is what the scientists inferred to be happening Balloon demo

North wasn’t always North!  Magnetic reversals  Looking at the rocks around these ridges we can see that the polarity in the rocks has switched.

Mid-Atlantic Ridge  This is a region of the Earth’s surface is also called a divergent plate boundary.

Divergent Plate boundary  What causes these plates to move?  – Drives these plates  Convection – Drives these plates Lava Lamp Lava Lamp

View of under the ocean