Zircons Are Forever

4.4 billion year record of oxygen isotopes in zircons

May 1 (Tuesday), 6 p.m., Teton Co. Library Auditorium –  “Zircons are forever: 4.4 billion year record of oxygen isotopes in zircons”. Presented by Liz King, Geologists of Jackson Hole.

Imagine reading a complex 450-page book that is missing the first 14 pages. And for the next 50 pages you only have words and incomplete sentences. Piecing together an accurate storyline would be difficult with such little information. Geologists face this challenge when piecing together Earth’s early history. There is one tool, remnant from that ancient time which still does exist, at least as far back as 4.4 billion of the earth’s 4.54 billion year history – zircon mineral grains.

Zircon is a common trace mineral in granitic rocks that preserves detailed records of magma genesis and is best known for its use establishing uranium-lead isotopic ages. Unlike uranium isotopes that decay through time, oxygen isotopes are stable but still a powerful tool for interpreting our planet’s history. Oxygen isotope ratios in zircon are most often used to interpret temperature history and magma source. No known rocks have survived from the first 500 million years of Earth history. The oldest known terrestrial samples are detrital zircons, separated from their parent igneous rocks by weathering and erosion. Studies of single zircons suggest that some continental crust formed as early as 4.4 billion years, 160 million years after accretion of the Earth. The oxygen isotope ratios in these zircons indicate the magmatic source came from evolved magmas with a protolith that interacted with liquid water at the surface of Earth. This talk will give a background of oxygen isotopes in zircons from younger rocks that allowed the interpretation of the world’s oldest mineral and the implications of liquid water on our planet 160 million years after the formation of our planet.