1. Iron Formations

2. From Meyers and Miller, 2008.

3. BIFs formed at the same time world wide.

4. BIFs http://www.geo.umn.edu/people/grads/bair0042/BIFs.jpg
Banded iron formation, iron and chert layers

5. Crusted plates collided and made the Great Lakes Tectonic Zone, which is still mildly active (still is possible to produce earthquakes).

6. Wait. Exam your bifs… what do you notice
Wait! Exam your bifs… what do you notice? …about their relative weight …are they magnetic?

7. Gravity Map, The iron formations are found by surveying the strength of the gravity and magnetic fields throughout Minnesota. Iron is more dense and magnetic than the surrounding layers.