Part 3, What does Plate Tectonics have to do with Climate?

1. Part 3, What does Plate Tectonics have to do with Climate? • Changes the topography • Changes the ocean circulation • Affects the re-cycling of volatiles • re-cycling of water vapor is particularly important on planets besides Earth, such as Mars, Venus & Io • In turn, climate affects the creation of continental crust & the long-term evolution of a planet

2. Changes in Ocean Circulation Earth: today - relatively cool • the arrangement of the continents affects circulation of the oceans • a different configuration of the continents leaves larger or smaller spaces in which water can circulate • more (less) efficient circulation may result in either cooler or (hotter) global weather Earth: Cambrian Era Earth: Jurassic - relatively hot note: take a look at Windows page on Geologic Time

3. Little Ice Age Example • Ice sheets used to cover the Great Lakes region • In the14th century the last of the retreating ice sheets freed the Lawrence waterway, allowing cold, glacial ice to drain into the North Atlantic • The influx of cold water decreased the average temperature in the North America and northern Europe by several degrees for a few centuries. • freezing temperatures at Valley Forge, Pennsylvania, for example note: take a look at Windows page on Geologic Time

4. Slippery Continents, a specialty of Earth, contributes to a recycling of volatiles • Hydrated minerals, such as kyanite, a biproduct of the breakdown of granite, help make the crust of the Earth “slippery”, and so facilitate the subduction of the plates • (unique to the Earth) • subducted plates are re-melted and returned to the surface as volcanoes • these re-release volatiles during eruptions

5. Plate Tectonics also forms New Crust • Over an extremely long time, plate tectonics forms the crust and shapes the surface of a planet. This process affects: (1) topography, as mentioned before (2) recycling of volatiles • In earliest days, Earth resembled Jupiter’s moon Io. The slow buildup of continental crust over Earth’s history shaped the course of its evolution.

6. How does That Work? • Silicate rocks are about 90% of the Earth’s surface. • They evolve in the magma chamber of a volcano. • (The exact chemistry will depend upon the pressure and temperature inside the chamber).

7. The Bowen Series shows the evolution of minerals in the chamber • The progression tend to separate light materials (silica-rich) from heavy materials (silica-poor). • The progression is well understood for the Earth. Efforts are underway to understand the progression for Mars.

8. Granite vs. Gabbro • Thus, the continental crust of the Earth is formed of light weight rocks such as granite (silica-rich). • The crust of the moon is made of more silicate-poor rocks such as gabbro. • The crust of Mars is made of basalt of an as-yet unknown silica %.

9. Subduction helps create new crust • The scraping of the crust as it subducts also creates a lightweight component of the crust which does not further subduct. • The lightweight component forms the continental crust of the Earth, crust which does not sink in the subduction process.

10. The Earth’s Surface has Evolved • Earliest Earth had no ocean, no continents, and an unknown atmosphere. • Continents grew, changed composition, and oxygen grew in the atmosphere. • Gradually the oceans have increased in saltiness as weathering of the surface proceeds. Earth: Jurassic - relatively hot Earth: Cambrian Era

11. Summary • Changes in topography and/or ocean circulation affect the way cooling and warming mechanisms of a region “work”. • Because climate affects the creation of continental crust, and vice-versa, a planet can get stuck with a single climate if there is no plate tectonics. • Can you name a few examples?

12. Part, 4; Plate Tectonics on Other Planets - Venus Venus - a thick atmosphere, no present-day plate tectonics • continents, volcanic rises, coronae • thick lithosphere (maybe) • lithosphere = frozen (maybe) • plate tectonics is not understood • there is some evidence of rifting & faulting

13. Cratering History& theories of catastrophic turn-over of the surface • The surface of Venus has just as few craters as does the Earth. This means that the surface is just as young as Earth’s surface! • Plate tectonics does not exist as it does on Earth, however. • Lithosphere is probably thick, not thin • Plates do not move. • Suggests a cataclysmic turn-over process may be at work. • The inside heats up until, POW! The whole surface melts.

14. Coronae & Island Arcs • There are features on the surface of Venus called “coronae” which strongly resemble terrestrial island arcs - a manifestation of plate tectonics

15. Volcanic Rises & Islands • On Earth, over a hot spot deep within, lava rises and creates a volcanic “island”. • Because of plate tectonics, the “island” moves away from the hot spot, gradually erodes away, and a new island takes its place. • On Venus, because of no plate motion, volcanic islands keep growing, and create giant continents instead. • These are called Volcanic Rises. Hot spot! (deep inside the Earth)

16. Mountains • Mountains of Venus are small, but the rock may be very dense. The crust may be very thick in order to support the weight. • On the other hand, the crust may be thin. • The uncertainties imply that the surface of Venus may turn over in a manner which is completely unlike that of the Earth.

17. Venus Climate • Venus has a thick, massive atmosphere. • Doesn’t seem capable of changing. • Theoretical work is on-going to test ideas of a changing climate. • What happens if there is a cataclysmic turn over of the surface - does that affect the atmosphere? • New results may suggest ways of measuring surface rock composition to seek evidence of climate change.

18. Mars Mars - a thin atmosphere, no present-day plate tectonics • continents, volcanic rises, magnetic stripes • thick lithosphere (maybe) • lithosphere = frozen in place • plate tectonics may have taken place in the past • there is some evidence of rifting & faulting

19. Volcanic Rise • The presence of a volcanic rise suggests a thick, and immobile lithosphere.

20. Magnetic Stripes • On Earth, the biggest proof of the mechanism of plate tectonics, sea-floor spreading, is in the striped ocean floor. • Mars has been found to have similar stripes, indicating plate tectonics in the past.

21. Martian “Geologic” Timeassociated with past Martian Plate Tectonics Like the Earth, Mars experienced “epochs” in its past history (like the Jurassic, or Cambrian), and these epochs have names! • Hesperian • When the super continent at the southern hemisphere formed • Something • 90% of the rest of martian history, when the cratering eased off