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Discovering the Oldest Piece of Earth
Aaron J. Cavosie
UPRM Geology
[email protected]
The first few hundred million years following accretion of the Earth is the least
understood eon in the geologic time scale: the Hadean. This poorly defined eon continues to both
challenge and fascinate scientists seeking to understand the early Earth, as the most profound
planet-wide transition in Earth history occurred during the Hadean: the post-accretion
transformation from a meteorite-impact-dominated, partially molten, steam-covered mafic
surface on a 'Hot Earth', to a solidified, granitoid-bearing, water covered, life-supporting 'Cool
Earth'. Intact rocks from the Hadean have not been identified; other means are thus required to
study early Earth processes, such as the appearance, formation, and processing of evolved crust,
duration of early impacts and magma oceans, the appearance of liquid water and oceans, and
ultimately, stabilization of habitats for life.
In 2001 I collected a rock called ‘quartzite’ from the Jack Hills in Western Australia, and
dated a few hundred detrital zircons from this rock. Thirteen years later, in 2014, colleagues and
I reported the remarkable discovery that this quartzite contained what is now recognized as
Earth’s oldest preserved material, a detrital zircon grain with a U-Pb age of 4374±6 Myr (= 4.4
Gyr). In this presentation I will discuss the geology of the site where the rock was collected, how
the discovery of the old zircon was made, why we waited so long to report this result, and what
this rare grain of sand tells geoscientists about the early Earth.