The picture of the early history of the Earth may soon be getting clearer.
A team from Louisiana State University (LSU) has found evidence showing that komatiites—three-billion-year old volcanic rocks found within the Earth’s mantle—had a different composition than modern ones, offering new information about the first billion years of Earth’s development and the early origins of life.
Researchers have been fairly uncertain about the evolution of Earth’s first 1.5 billion years, largely due to a lack of any significant rock record prior to four billion years ago and a very limited record until about three billion years ago.
Rocks this age are generally extensively altered, making comparisons to modern rock difficult.
The new insight is a result of three decades of LSU scientists studying and mapping the Barberton Mountains of South Africa. The researchers conducted chemical analyses of hundreds of komatiite rocks sampled from about 10 lava flows.
“Early workers had mapped large areas incorrectly by assuming they were correlatives to the much more famous Komati Formation in the southern part of the mountains,” LSU geology professor Gary Byerly said in a statement. “We recognized this error and began a detailed study of the rocks to prove our mapping-based interpretations.”
The researchers discovered original minerals called fresh olivine within the rocks. While rarely found in rocks, fresh olivine is a major constituent of Earth’s upper mantle and controls the nature of volcanism and tectonism of the planet.
“Discovering fresh unaltered olivine in these ancient lavas was a remarkable find,” geology Ph.D graduate Keena Kareem said in a statement. “The field work was wonderfully productive and we were eager to return to the lab to use the chemistry of these preserved olivine crystals to reveal clues of the Archean Mantle.”
The researchers said that a chunk of early-Earth magma ocean could be preserved in the approximately 3.2 billion year-old minerals.
“The modern Earth shows little or no evidence of this early magma ocean because convection of the mantle has largely homogenized the layering produced in the magma ocean,” Byerly said. “Oxygen isotopes in these fresh olivines support the existence of ancient chunks of the frozen magma ocean.
“Rocks like this are very rare and scientifically valuable. An obvious next step was to do oxygen isotopes,” he added.
The study was published in Nature Geoscience.
