[Rockhounds] Earth's 1st continents arose hundreds of millions of years earlier than thought

[Kreigh Tomaszewski]

Earth's first continents, known as the cratons, emerged from the ocean
between 3.3 billion and 3.2 billion years ago, a new study hints.

This pushes back previous estimates of when the cratons first rose from the
water, as *various* <https://pubmed.ncbi.nlm.nih.gov/29795252/> *studies*
<https://www.researchgate.net/publication/225191729_44_billion_years_of_crustal_maturation_Oxygen_isotope_ratios_of_magmatic_zircon>
suggested
that large-scale craton emergence took place roughly 2.5 billion years ago.

"There was no uncertainty that continents were partly sticking out of water
as early as 3.4 billion years ago," said Ilya Bindeman, a professor of
geology at the University of Oregon, who was not involved in the new study.
That's because scientists have found sedimentary rocks — which form from
the broken-up bits of other rocks that have undergone erosion and
weathering — that date back to that era. Such sedimentary rocks could only
form once land broke through the surface of early *Earth*
<https://www.livescience.com/earth.html>'s oceans.

But although geologists knew that at least part of the cratons must have
been exposed more than 3 billion years ago, the exact timing and extent of
their emergence remained a matter of debate, Bindeman told Live Science in
an email. The study authors suggest that entire cratons, not just small
patches of land, emerged from the oceans 3.3 billion years ago, even though
the planet then lacked the "modern-style *plate tectonics*
<https://www.livescience.com/crystals-reveal-plate-tectonic-age.html>"
needed to drive those floating bits of crust upward, he said.

For the new study, published Nov. 8 in the journal *Proceedings of the
National Academy of Sciences*
<https://www.pnas.org/cgi/doi/10.1073/pnas.2105746118> (PNAS), the authors
trekked to the Singhbhum Craton, located in eastern India. "Pockets" of
ancient sedimentary rocks had previously been found at the craton, and the
team wanted to determine their exact ages and the nature of how they
formed, said first author Priyadarshi Chowdhury, a postdoctoral research
fellow at Monash University's School of Earth, Atmosphere and Environment
in Melbourne, Australia.

"When we joined all the sedimentary pockets together, we found that all of
them kind of formed simultaneously," in river or beach-like environments,
Chowdhury told Live Science. That would imply that much of the craton
became exposed to air and running water at the same time. "That was like
the point when we realized, okay, we are onto something."

https://www.livescience.com/earth-first-continents-cratons-study