2015 Colby Geology T-shirts are in. Designed by June Li '16, they're $10 each in the Geo Dept. office

This Friday's Seminar SpeakerThis Friday's Seminar Speaker::

Dr. Timothy McCoyDr. Timothy McCoyCurator-in-Charge of the Meteorite CollectionCurator-in-Charge of the Meteorite Collection

Smithsonian InstitutionSmithsonian Institution

Four Cores, 5 Missions and Four Cores, 5 Missions and 10,000 Meteorites Ago: What is 10,000 Meteorites Ago: What is

Inside Planets?Inside Planets?

1:00 p.m.1:00 p.m. Keyes 105Keyes 105

Japan's Mount Aso erupted on Monday, Sept. 14th, sending clouds of volcanic ash kilometers into the sky and forcing the evacuation of dozens of hikers and tourists.

Also on Monday, flash flooding near the Utah-Arizona border has left sixteen people dead and at least five more missing.

Geology in the news ...

What does the winter hold in store for us?

PLATE TECTONICS andPLATE TECTONICS andCONTINENTAL DRIFT - Part 1CONTINENTAL DRIFT - Part 1

This has This has REVOLUTIONIZEDREVOLUTIONIZED the Earth Sciences the Earth Sciencesmuch the way Darwin and Natural Selection did tomuch the way Darwin and Natural Selection did to

biology in the 19th century.biology in the 19th century.

The earliest The earliest mapmakers noticed mapmakers noticed

the apparentthe apparentclose fit of continental close fit of continental

margins.margins.

As map making improved, the possible fits of the As map making improved, the possible fits of the continents were noted by Francis Bacon (1561- continents were noted by Francis Bacon (1561- 1626), George Buffon (1707-1788), and 1626), George Buffon (1707-1788), and Alexander von Humboldt (1769-1859)! This isn't Alexander von Humboldt (1769-1859)! This isn't new!new!

BUT ….BUT ….With better, With better, modern mapping - modern mapping - the fit got even the fit got even better yet! - about better yet! - about 96% perfect!96% perfect!

Alfred WegenerAlfred Wegenerproposed in 1912 that the proposed in 1912 that the continents were not only continents were not only moving, but actually plowing moving, but actually plowing through the sea floor.through the sea floor.

The leading physicists of his day, however, were The leading physicists of his day, however, were able to show that this was physically not able to show that this was physically not possible. The proposed possible. The proposed mechanismmechanism was thus was thus discredited, so the entire hypothesis was set discredited, so the entire hypothesis was set aside (by most!) as yet more wishful thinking.aside (by most!) as yet more wishful thinking.

Now, however, plate tectonics is accepted Now, however, plate tectonics is accepted by most of the scientific community as by most of the scientific community as beyond significant doubt.beyond significant doubt.

BASIC PREMISEBASIC PREMISE::The Earth's surface is comprised of 7 The Earth's surface is comprised of 7

major plates, and about 20 minor major plates, and about 20 minor plates, that behave as relatively brittle plates, that behave as relatively brittle slabs, called slabs, called LITHOSPHERELITHOSPHERE. They . They move over slow flow in an underlying move over slow flow in an underlying plastic layer, the plastic layer, the AESTHENOSPHEREAESTHENOSPHERE..

The plates of theThe plates of the LITHOSPHERE LITHOSPHERE are ~100-150 km thick, but rigid are ~100-150 km thick, but rigid..The The AESTHENOSPHERE AESTHENOSPHERE is plastic (soft and deformable) and generally is plastic (soft and deformable) and generally

200-400 km thick.200-400 km thick.

NOTE that these lithospheric plates are mostly mantle, with the crust carried along on top.

Note that Iceland is split between TWO plates!

SO, what's the SO, what's the EVIDENCEEVIDENCE ????????

1.1. Matching geology Matching geology across areas of across areas of apparent fit apparent fit

This even includes matching mountain belts!This even includes matching mountain belts!

Lystrosaurus, a primitive Triassic reptileLystrosaurus, a primitive Triassic reptile

Glossopteris, a primitive seed fern, ancestor of flowering plantsGlossopteris, a primitive seed fern, ancestor of flowering plantsspecimen from Africa specimen from Australia

2.2. Matching fossils distributed across areas of proposed fit. Matching fossils distributed across areas of proposed fit.

This is significant because …. This is significant because …. the the MODERNMODERN natural natural biotas are completely different!biotas are completely different!

Monkeys that have Monkeys that have prehensile tails are prehensile tails are found only in the New found only in the New World…. while the World…. while the Great Apes Great Apes are only are only found in the Old World.found in the Old World.

ForFor exampleexample, , thethe plant family Cactaceae plant family Cactaceae (the cacti) is native (the cacti) is native onlyonly in the Western in the Western Hemisphere, while the Hemisphere, while the shrubs and trees of shrubs and trees of EucalyptusEucalyptus are found are found naturally only in naturally only in Australia Australia

3.3. Glacial geologic matching in ancient rocks - of glacial patterns Glacial geologic matching in ancient rocks - of glacial patterns that make absolutely that make absolutely nono sense sense unless the continents WERE unless the continents WERE connected in the past, as matching margins suggest they were.connected in the past, as matching margins suggest they were.

[ Oorlogskloof Nature Reserve,South Africa ]

4.4. Paleomagnetic signatures in rocks of the sea floor... Paleomagnetic signatures in rocks of the sea floor...

... supplemented by demonstrably ... supplemented by demonstrably greater sea-floor ages the farther greater sea-floor ages the farther one is from the center.one is from the center.

5.5. "Polar wandering" curves - those from North America "Polar wandering" curves - those from North America and Europe are very different. BUT there's only one northand Europe are very different. BUT there's only one north pole in the world!pole in the world!

This apparent discrepancy This apparent discrepancy ONLY makes sense if you ONLY makes sense if you allow the continents to allow the continents to move.move.

6.6. We now even have very accurate GPS measurements that We now even have very accurate GPS measurements that show how fast the plates are actually moving - DIRECTLY!show how fast the plates are actually moving - DIRECTLY!

http://xenon.colorado.edu/spotlight/index.php?action=kb&page=3

This is driven by CONVECTION in the mantle, This is driven by CONVECTION in the mantle, produced by heat from deep within the Earth.produced by heat from deep within the Earth.

Soooo, how does this Soooo, how does this workwork??

If we look at the ocean floor, we see: If we look at the ocean floor, we see:

This mountain range is called theThis mountain range is called theMid-Oceanic Rise and Ridge System (MORRS)Mid-Oceanic Rise and Ridge System (MORRS)

If we look closely at the MORRS, we see this topography If we look closely at the MORRS, we see this topography

The increased age of rocks from the center outwards The increased age of rocks from the center outwards implies the ridge in the center is expanding outwards, implies the ridge in the center is expanding outwards, pushing the continents apart as it grows.pushing the continents apart as it grows.

This is called a This is called a Zone of DivergenceZone of Divergence of lithospheric plates. of lithospheric plates.

BUTBUT, , if this is happening, either ...if this is happening, either ...

… … the Earth must be getting larger and the Earth must be getting larger and

larger,larger, OR …….OR …….

Something has to be destroyed somewhere else!Something has to be destroyed somewhere else!This occurs in This occurs in Zones of Plate Zones of Plate ConConvergencevergence

Type I: oceanic lithosphere is Type I: oceanic lithosphere is subductedsubducted beneath a continental beneath a continental

margin (an margin (an Andean-type subduction zoneAndean-type subduction zone))

"Subduction leads to orogeny.""Subduction leads to orogeny."

This process also generates a great deal of heat, which This process also generates a great deal of heat, which melts rocks, producing melts rocks, producing magmamagma. We'll come back to this.. We'll come back to this.

This subduction process creates earthquakes, This subduction process creates earthquakes, defining a plane called a defining a plane called a Benioff-Wadati ZoneBenioff-Wadati Zone..

This subduction is This subduction is evident in the evident in the increasing depth of increasing depth of earthquake origins earthquake origins (foci) inland - (foci) inland - which is how this which is how this hypothesis hypothesis originated in the originated in the first place.first place.

Earthquake origins off the Earthquake origins off the coast of Kamchatka show coast of Kamchatka show this pattern, including one on this pattern, including one on February 10th, 2004, marked February 10th, 2004, marked by the green star.by the green star.

FRIDAY:FRIDAY:The drama continues:The drama continues:

WHY? HOW? WHY? HOW? mountain building,mountain building,

earthquakes, & earthquakes, & volcanoes - oh my!volcanoes - oh my!