Was the Early Earth Habitable Brooke Norsted University

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 activity Tour of Earth’s oldest rocks Current research about the early Earth

How do we know?

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 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.

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

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…

Acasta Gneiss 4. 03 billion years old

Nuvvuagittuq Greenstone Belt 3. 8 to 4. 28 billion years old

Isua Greenstone Belt 3. 7 -3. 8 billion years old

Morton Gneiss 3. 53. 7 billion years old

Ancient Gneiss Complex 3. 4 -3. 5 billion years old

Narryer Gneiss Terrane 3. 4 -3. 6 billion years old

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!

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.

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

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

Put it in the SHRIMP (Sensitive High Resolution Ion Micro. Probe)