Chapter 17 Notes Section 2

II. SeaFloor Spreading - proposed by Harry Hess in 1962 (the o.. floor is riftingapart at the center of all the o..)

A- Mapping the Ocean Floor -

1- Magnetometer - measures the m.. fieldin the rocks on the o.. floor.

2- Sonar - bounces s.. waves off the oceanfloor to measure the d.. and therefore thetopography.

B- Ocean Floor Topography -

1- Mid-Ocean Ridges - underwater m..chains found at the center of all the o…a- 65,000 km long and as high as 3 km.b- Earthquakes & Volcanoes - are

common.

2- Deep-Sea Trenches - narrow,elongated c.. in the sea floor.a- they can be - 1000’s of km long

and as much as 11 km deep(Mariana Trench)

C- Ocean Rocks & Sediment -

1- Age of Rocks - increases as distance i.. fromthe mid-ocean ridges.

a- Symmetrical - and parallel on both sides of the m..-o.. ridges.

b- Oldest Seafloor Rocks - only 180 myo, Why??

2- Thickness of Sediments - increases as thedistance i.. from the m..-o.. ridges. Why?

D- Magnetism- a magnetic field is g.. by the Earth’s outer molten core as the Earth r…

1- Magnetic Reversal - when the o.. core switches d.., the m.. poles switch.

a- Normal Polarity - is the Earth’s present o..b- Reversed Polarity - is opposite to today’s

2- Paleomagnetism- the study of the Earth’s m.. f… history.a- Iron-Bearing Magnetite - crystals align

with the m.. field when the lava c..

3- Magnetic Symmetry - magnetic orientationform a matching pattern on both sides of the m..- o.. ridges (magnetic stripes)

4- Isochron - an imaginary line on a m.. thatshows points that have the same a..

E- Seafloor Spreading - new o.. crust isformed at the o.. r.. and moves in opposited…

1- Subduction - the old o.. crust is pushed downinto the m.. where it is r…

2- Acts like - a “conveyor belt”

http://www.youtube.com/watch?v=gVToWuG2QIA