WARC DISCOVERIES

Lithium in the world’s oldest minerals indicate an active weathering cycle in the first few hundred million years of Earth’s history

Lithium is an element that is highly mobile in low-temperature, aqueous weathering environments.  WARC researchers Takayuki Ushikubo, Noriko Kita, and John Valley, along with collaborators Aaron Cavosie, Simon Wilde, and Roberta Rudnick analyzed Li concentrations and isotopic compositions in the world’s oldest minerals, the famous >4 billion-year-old zircons from the Jack Hills, Western Australia.  In their paper in Earth and Planetary Science Letters, WARC researchers document relatively high lithium abundances that are indicative of low-temperature aqueous weathering environments, as well as lithium isotope compositions that are similar to continental crust weathering products.  These new results indicate the presence of an active continental weathering cycle in the earliest Earth that produced >4.3 billion-year-old sedimentary rocks that were enriched in Li and had variable Li isotope compositions; subsequently, these sedimentary rocks were incorporated into continental magmas that crystallized zircon, trapping the record of this earlier weathering period.  These new results confirm previous evidence for liquid water on the Earth’s surface >4.3 b.y. ago, which was based on oxygen isotope data obtained on the same Jack Hills zircons.

Citation:
Ushikubo, T, Kita, NT, Cavosie, AJ, Wilde, SA, Rudnick, RL, and Valley, JW (2008) Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust.  Earth and Planetary Science Letters 272:666-676.  A PDF copy of the paper can be found here.

Posted August 27, 2008