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For the next hour…

Was the Early Earth Habitable? Brooke Norsted University of Wisconsin Geology Museum www.geologymuseum.org brooke@geology.wisc.edu. For the next hour…. Radiometric dating Radiometric dating activity Tour of Earth’s oldest rocks Current research about the early Earth. How do we know?.

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For the next hour…

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  1. Was the Early Earth Habitable? Brooke NorstedUniversity of Wisconsin Geology Museumwww.geologymuseum.orgbrooke@geology.wisc.edu

  2. For the next hour… Radiometric dating Radiometric dating activity Tour of Earth’s oldest rocks Current research about the early Earth

  3. How do we know?

  4. Radiometric dating –The right tool for the right job • Not just U-Pb… There are 40 different dating techniques and each one has an appropriate use • uranium-lead (between 1 million – 4.5 billion years) • radiocarbon (between present – 45,000 years) • Multiple techniques can be used on the same sample to get more reliable dates • (e.g. use Uranium-Lead and Potassium-Argon). • More than one mineral can be tested from one sample to get a more reliable date.

  5. Activity Instructions • Groups of 2-3 people • Materials – data sheet and graph, bag of M&M’s (NOT for eating… yet) and a writing utensil • We will go through six half-lives, measuring how many parent nuclides are left after each round • Starting at T=0 with 100 parent nuclides • “M” side up = parent nuclide

  6. Graph three lines • Your group’s data • The class average data • A “perfect” half life • T=1  50 • T=2  25 • T=3  12.5 • Etc…

  7. Acasta Gneiss 4.03 billion years old

  8. Nuvvuagittuq Greenstone Belt 3.8 to 4.28 billion years old

  9. Isua Greenstone Belt 3.7-3.8 billion years old

  10. Morton Gneiss 3.5-3.7 billion years old

  11. Ancient Gneiss Complex 3.4-3.5 billion years old

  12. Narryer Gneiss Terrane 3.4-3.6 billion years old

  13. What do we know from radiometric dating? • Oldest known rocks on earth are 4.03 billion years old • Meteorites are all around 4.56 billion years old and give us our best handle on the limits of the age of our solar system, and the Earth • But wait, there’s more old stuff!

  14. Jack Hills Metaconglomerate 3.0 billion years old (part of the Narryer Gneiss Terrane in Western Australia) Conglomerates are a sedimentary rock, made of bits of other rocks and minerals that get cemented together. Think concrete. Metaconglomerates are conglomerates that have been metamorphosed.

  15. Why zircons? • Zircons are everywhere • They form in igneous and metamorphic rocks and then erode and are incorporated into sedimentary rocks • Zircons are tough • They are hard and can survive intact as the rest of the rock around it erodes. Then they can be transported and incorporated into sedimentary rocks. • Zircons are good for radiometric dating • When they form in igneous and metamorphic rocks, they pull radioactive parent nuclides (isotopes) into their crystal structure like Uranium 238, Uranium 235 and Thorium 232

  16. How to date a zircon 2. Separate zircons from other minerals 1. Crush sample 3. Isolate zircon crystals

  17. Put it in the SHRIMP (Sensitive High Resolution Ion MicroProbe)

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