Download Ch. 17 Sec. 2

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

Magnetic stripe card wikipedia , lookup

Neutron magnetic moment wikipedia , lookup

Electromagnetic field wikipedia , lookup

Giant magnetoresistance wikipedia , lookup

Magnetic monopole wikipedia , lookup

Magnetometer wikipedia , lookup

Magnetotactic bacteria wikipedia , lookup

Electromagnet wikipedia , lookup

Magnet wikipedia , lookup

Earth's magnetic field wikipedia , lookup

Ferrofluid wikipedia , lookup

Force between magnets wikipedia , lookup

Magnetohydrodynamics wikipedia , lookup

Magnetoreception wikipedia , lookup

Magnetochemistry wikipedia , lookup

Magnetism wikipedia , lookup

Multiferroics wikipedia , lookup

Magnetotellurics wikipedia , lookup

Ferromagnetism wikipedia , lookup

Geomagnetic reversal wikipedia , lookup

History of geomagnetism wikipedia , lookup

Transcript
Ch. 17 Sec. 2
Sea Floor Spreading
Technology
Until the mid 1900’s, scientists believe that the ocean
floor was flat
 Sonar helped change the ideas and map the ocean
floor



Sound waves bouncing back from the floor
Magnetometer detects small changes in magnetic
fields
Ocean floor Topography
Maps made from sonar & Magnetometer really
stunned scientists
 Noticed many trenches and volcanoes



Common along ocean ridges
Mariana Trench: 11 km deep
Ocean Rocks
Scientists collected samples of the deep-sea sediments
 1st: Ages of rocks vary from place to place



Rocks near ocean ridges are younger that those taken by
trenches
2nd: Thickness of ocean-floor sediments is less than
predicted


Continental Crust is extremely thick, 20 km or so
Thickness of the sediments increased further from ridges
Magnetism
Oceanic rock contains iron-bearing materials
 Paleomagnetism: study of magnetic record




Basalt provides an accurate record of ancient magnetism
As Basalt cools, materials become parallel with the ridges
Magnetic Reversal: change in earth’s magnetic field


As the sea floor spreads, so too the magnetic field is reversed
Long change in earth’s magnetic field is Epochs
Magnetic Symmetry
Noticed a series of + and – strips
 Help to create Isochron Maps


Line on a map that connects points that have the same age
Sea-Floor spreading

Harry Hess proposed the theory


New ocean crust formed at the ocean ridges and destroyed
and deep trenches
Magma forced up, hotter & less dense than mantle material,
fills the gap created at the ocean ridges
Sea-floor spreading was the missing link for
Wegener’s Continental Drift theory
 Answers the how question, but not the why
