1 / 24

Radioactive Decay and Thermal Convection


Radioactive Decay and Thermal Convection
. Thermal structure of the Earth: Heat is a driver for seismological processes. Starting with student experiences. What evidence do they have for Earth’s internal temperature?. Starting with their experiences.

cecilia-silva
Download Presentation

Radioactive Decay and Thermal Convection


An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radioactive Decay and Thermal Convection


  2. Thermal structure of the Earth: Heat is a driver for seismological processes

  3. Starting with student experiences What evidence do they have for Earth’s internal temperature?

  4. Starting with their experiences

  5. Earth’s heat and the age of the Earth • Uniformitarianism (Lyell’s Principles of Geology) • same geological processes occurring today have existed throughout geologic time • Darwin (Origin of Species) estimated that it took 300 million years to erode a chalk deposit in southern England • Lord Kelvin - estimate time from molten state to solidification via cooling • temperature at Earth's core = melting point of rocks • temperature gradient with regard to depth below the surface (1 degree/50’) • thermal decrease through conductivity of rocks* • Estimate of 20 myo to 400 myo)

  6. Challenges to Kelvin’s model • Assumption of a solid Earth • Some argued that the Earth had never been a molten sphere; rather Earth had formed from the slow accumulation of solid material like asteroids. • Some attacked Kelvin's assumption about a closed system of dwindling initial heat • Others offerred the possibility that the then-unknown internal structure of atoms could contain massive amounts of potential energy

  7. Where does the heat come from? • 20% Residual heat from accretion and gravitational collapse • 80% Radioactive decay • Uranium-238 (4.47 × 109) • Uranium-235 (7.04 × 108) • Thorium-232 (1.40 × 1010) • Potassium-40 (1.25 × 109)

  8. Average 25oC/km

  9. Thermal structure Tufts.edu

  10. Earth’s Energy Budget • Solar Radiation - (99.978%, or nearly 174 petawatts; or about 340 W m-2) • Geothermal Energy - (0.013%, or about 23 terawatts; or about 0.045 W m-2) • Tidal Energy – (0.002%, or about 3 terawatts; or about 0.0059 W m-2). • Waste Heat - (about 0.007%, or about 13 terawatts; or about 0.025 W m-2)

  11. How is Earth’s heat released? • Conduction • Convection • Sketch expected convection in pan

  12. How to best model mantle material • Obleck? • Cornstarch and water • Silly putty? • What are important criteria for choosing?

  13. Convection and Earth’s interior

  14. 3D Mantle flow models

  15. 3D Mantle flow models

  16. Mantle convection • Can be imaged using seismic waves • Complex • Sometimes both upper and lower mantle together • Some subduction zones can be imaged to base of mantle

  17. Reflection on Earth’s interior • First by yourself, and then with your table, consider 1, 2 or all 3 of the following questions: • What is the difference between the crust and the mantle? • What is the difference between the lithosphere and the asthenosphere? • Why are both sets of terms used, and which would be simplest for your students to understand?

More Related