Plate Tectonics A.What are the lines of evidence Wegener used to support Continental Drift? B.What is seafloor spreading? How do transform faults behave.

Plate TectonicsA. What are the lines of evidence

Wegener used to support Continental Drift?

B. What is seafloor spreading? How do transform faults behave oddly at the Mid-Ocean Ridge?

C. What was the key development that led to our current theory of Plate Tectonics?

Drift Rejection Question

• It shows that science is based much off logic and reason, and if a "proof" can not be logically proved, then it can be rejected regardless if it is true or false.

Drift Rejection Question

• It shows that without enough evidence, only guesses can be made about why things occur. The scientists just didn't have enough evidence that could explain why things were the way they were. Now days we have satellites, and submersibles and other types of data collecting devices which helps us see the bigger picture.

Drift Rejection Question

• It shows that through proving things wrong, scientists are getting closer to the truth. Wegener had hypotheses that were eventually proved wrong, but knowing that those hypotheses are wrong narrows down the answers to the correct answer.

Drift Rejection Question

• The story indicates that science is a complex subject in itself and when one hypothesizes about something they must have evidence to support what their findings and results show. There has to be plausible explanation as to why the hypothesis makes sense ... however, that's only a start and a lot more has to be proven before the hypothesis is accepted as a theory.

In a nutshell...

•“Extraordinary claims require extraordinary evidence” - Carl Sagan

Review of Plate Tectonics

• What drives Earth processes?– gravity and density differences– external (e.g. hydrologic cycle, erosion)– internal (e.g. mantle convection)

Plate Boundaries

• divergent (AKA constructive)• transform• convergent (AKA destructive)

– ocean-ocean (e.g. Mariana Islands)– ocean-continent (e.g. Pacific-North

America)– continent-continent (e.g. India-Asia)

Examples

• divergent (e.g. mid-Atlantic ridge)• transform (e.g. San Andreas fault

zone)• convergent

– ocean-ocean (e.g. Pacific-Pacific near Marianas Islands)

– ocean-continent (e.g. Pacific-North America)

– continent-continent (e.g. India-Asia)

Examples

• divergent (e.g. mid-Atlantic ridge)• transform (e.g. San Andreas fault

zone)• convergent

– ocean-ocean (e.g. Pacific-Pacific near Marianas Islands)

– ocean-continent (e.g. Pacific-North America)

– continent-continent (e.g. India-Asia)

Examples

• divergent (e.g. mid-Atlantic ridge)• transform (e.g. San Andreas fault

zone)• convergent

– ocean-ocean (e.g. Pacific-Pacific near Marianas Islands)

– ocean-continent (e.g. Pacific-North America)

– continent-continent (e.g. India-Asia)

Plates?

Plate

QuestionsSea floor spreading explains all EXCEPT which of

the following observations:

1. chains of oceanic islands

like Hawaii 57%

2. the young age of oceanic crust 6%

3. increasing age of oceanic crust

away from ridge crests 2%

4. Benioff zone of earthquakes

descending from oceanic trenches 28%

5. Rift valley at mid-ocean ridges 7%

Polarity Question

The portion of the ocean crust nearest the mid-ocean ridge must have what type of magnetic polarity?

1. normal 63%

2. reverse 28%

3. none 9%

Estimation Question

• How many kilometers has India pushed its way into the soft underbelly of Asia in the last 55 million years?

1. 2750 cm 6%2. 2.75 km 18%3. 275 km 25%4. 2750 km 37%5. 2750 m 7%6. 27500 km 7%

~800 km

Estimation Question

• How many kilometers has India pushed its way into the soft underbelly of Asia in the last 40 million years?

• 55,000,000 yr x 5cm/yr x 1m/100cm x 1km/1000m = 2750 km

Another one:

• Los Angeles is on the west side of the main San Andreas fault system. Movement along the fault is carrying LA northwest (with respect to North America) at a rate of approximately 3 cm/year.

• a) Assuming that the motion will continue in the same direction and at the same rate for the next 300 million years or so, how many kilometers will Los Angeles have traveled in 27 million years?

Continued…

• b) In its travels, Los Angeles won’t collide with anything for about 4000 km. How far in the future will this be?

• c) When it does collide, who will be the lucky owners of a new accreted terrane?