An analysis of rock samples collected from the Superior Province, the region in Canada just north of the Great Lakes, suggests the samples contain components of ancient basaltic crust that existed more than 4.2 billion year ago (Hadean eon).
Recreating the nature of Earth’s first crust is difficult because geologic activity has created turnover that drove most of it back into Earth’s interior.
While some slivers of 4-billion-year-old crust remain in the rock record, only isolated zircon mineral grains are dated to be older.
“Finding remnants of early Earth’s crust has proven difficult, but a new approach offers the ability to detect the presence of truly ancient crust that has been reworked into ‘merely’ really old rocks,” said study co-author Dr. Richard W. Carlson, Director of the Department of Terrestrial Magnetism at the Carnegie Institution for Science.
The novel approach examines variations in the abundance of an isotope of the element neodymium, which is created by the radioactive decay of a different element, samarium.
The isotope of samarium with a mass of 146 (samarium-146) has a half-life of only 103 million years. It decays to the isotope of neodymium with a mass of mass 142.
While samarium-146 was present when Earth formed, it became extinct very early in Earth’s history.
Researchers know of its existence from the study of very ancient rocks, especially meteorites and samples from Mars and the Moon.
Variations in the relative abundance of neodymium-142 compared to other isotopes of neodymium that didn’t originate from decaying samarium reflect chemical processes that changed the ratio of samarium to neodymium in the rock while samarium-146 was still present–basically before about 4 billion years ago.
Dr. Carlson and his colleague, University of Ottawa researcher Dr. Jonathan O’Neil, studied 2.7 billion-year-old granitic rocks that make up a…