Download Earth`s Magnetic Field

Worldwide seismicity from 1 January 2007 to 1 June 2007. Source: USGS National
Earthquake Information Center.
Earth’s
Magnetic
Field
http://www.earthweek.com/2011/ew110311/ew110311h.jpg
http://science.nasa.gov/media/medialibrary/2003/12/22/29dec_magneticfield_resources/nmppath2001_med.gif
Magnetization of
Magnetite
Lavas record
magnetic
reversals
Magnetic
reversals
over the past
20 million
years
Magnetic time scale
•
•
•
•
0-700,000 -- Normal
700,000 - 2.5 my -- Reversed
> 2.5 my -- Normal
Ko`olau lavas mostly reversed in polarity,
so they must be older than 700,000 yrs,
but younger than 2.5 my
• Lavas on Kaua`i and in Wai`anae Range
show normal polarity, so they must be
older than 2.5 my
__________ 1. According to the concepts of plate tectonics, the continents of
Africa and South America are gradually approaching each other.
__________ 2. Most geologists believe that continents are larger now than
they were in the past.
__________ 3. The size of the earth is gradually increasing over time because
of seafloor spreading.
__________ 4. Tectonic plates drift in oceans of melted magma just below the
surface of the earth.
__________ 5. When two oceanic plates collide, the colder denser older plate
is stronger and subducts the newer warmer plate.
Maps recording the locations of earthquakes
around the world show that
1. earthquakes are evenly distributed.
2. most earthquakes follow the border of the
Atlantic Ocean.
3. most earthquakes occur in the interior of
continents.
4. most earthquakes surround the Pacific Ocean.
The lithosphere is composed of:
1.
2.
3.
4.
Core and mantle
Crust and asthenosphere
Crust and uppermost mantle
Core and asthenosphere
Sea-floor spreading suggests that
1. the sea floor moves away from the mid-ocean
ridge.
2. the sea floor moves toward the trenches.
3. the sea floor age increases from mid-ocean
ridge to the continents.
4. all of the above are true.
Most plates move at an average rate that is
best described by which unit rate?
1. cm/year.
2. m/year.
3. km/year.
4. plates don’t move.
If you dredged a sample of volcanic rock from
locality X, the most likely age of the rock (in
other words, the amount of time elapsed since
the rock cooled from a magma) would be:
1. 1 year
2. 1 million years
3. 10 million years
4. 100 million years