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Where do those plate reconstructions through time come from?. What data is used to make these reconstructions? Paleomagnetism, paleoclimates, rock distributions, biogeographic distribution of organisms. Polar Wandering.
What data is used to make these reconstructions?
Paleomagnetism, paleoclimates, rock distributions, biogeographic distribution of organisms
Along with sea floor spreading, “APW curves” are the two data sets that lead to the development of the theory of plate tectonics
The basics of
Field lines “come to closure” at the geographic north pole, which
is why compasses point here. What does that say about the
orientation of the earth’s dipole in the core? Yes, the south end of
the dipole is pointing north!
that field lines are oriented at different angles relative to the
Earth’s surface; parallel at the equator, perpendicular at the
poles, approx. 45 degrees at 45 degrees N or S latitude.
South end of the dipole (our geographic North pole) AND
vertically, parallel to the field orientation relative to the
surface of the earth = angle of inclination
and angle of
When magma cools the iron present in mafic minerals orient
parallel to the field lines at that time and place
Curie Point is
for the temp.
iron-rich grains settle out of the water, if the water is “quiet” they
will orient themselves parallel to the earth’s magnetic field. Of
course, the grains may be disturbed after deposition (by burrowing
organisms, for example, so the paleomagnetic signal out of these
rocks is often less reliable.
the latitude on the Earth’s surface where an Fe-rich rock
formed, we can use this information to determine the “paleo-
latitude” for an iron-rich rock.
British geophysicists measured the
angles of inclination of Fe-
rich rocks of a wide range of
ages. What did they find?
Each rock recorded a different angle
How did they interpret this data:
from one time period to another,
the Earth’s magnetic field moved =
Of course, if the continents where you sampled the rocks are going to
remain stationary, then the pole must be moving, or wandering
Which interpretation is correct? What happens if you sample rocks from a different continent?
Rocks of the same age from different continents record two different magnetic
poles! In green is shown where rocks from Eurasia say the magnetic pole
should be, and in red are the data points from North America. Obviously,
there is only 1 magnetic pole, so if you move the continents together, the
lines tracing the location of the magnetic pole through time for these two
continents coincide. Thus, it must be the continents that moved, not the poles!
Thus, proving that the poles have not moved over the Earth’s surface over time, but the continents moved, re-focused attention on the idea of “continental drift” only now there was a completely new data set from the ocean floor as well: sea floor spreading
Sea floor spreading: new ocean crust is created at ridges and old crust is destroyed at trenches. The sea floor is continually “recycling” material from the mantle.
The theory of plate tectonics synthesizes the two theories of continental
drift and sea floor spreading
The fact that they shared the same marine animals suggests that
the Iapetus Ocean was narrow at this time
Laurentia to be?
Strength decreases slowly, rapid change in polarity, strength