Was the Early Earth Habitable

1. Was the Early Earth Habitable?
Brooke Norsted
University of Wisconsin Geology Museum
www.geologymuseum.org
brooke@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?

8. 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.

9. 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

10. 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…

14. Acasta Gneiss
4.03 billion years old

16. Nuvvuagittuq Greenstone Belt
3.8 to 4.28 billion years old

18. Isua Greenstone Belt
3.7-3.8 billion years old

20. Morton Gneiss
3.5-3.7 billion years old

22. Ancient Gneiss Complex
3.4-3.5 billion years old

24. Narryer Gneiss Terrane
3.4-3.6 billion years old

26. 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!

28. 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.

29. 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

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

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