1.5 billion-year-old Earth had water everywhere, but not one continent, study suggests

Water, water, everywhere.
Water, water, everywhere. (Image credit: Shutterstock)

What did Earth look like 3.2 billion years ago? New evidence suggests the planet was covered by a vast ocean and had no continents at all.

Continents appeared later, as plate tectonics thrust enormous, rocky land masses upward to breach the sea surfaces, scientists recently reported.

They found clues about this ancient waterworld preserved in a chunk of ancient seafloor, now located in the outback of northwestern Australia. 

Related: Photo timeline: How the Earth formed

Around 4.5 billion years ago, high-speed collisions between dust and space rocks formed the beginnings of our planet: a bubbling, molten sphere of magma that was thousands of miles deep. Earth cooled as it spun; eventually, after 1,000 to 1 million years, the cooling magma formed the first mineral crystals in Earth's crust.

Meanwhile, Earth's first water may have been carried here by ice-rich comets from outside our solar system, or it may have arrived in dust from the cloud of particles that birthed the sun and its orbiting planets, around the time of Earth's formation. 

When Earth was a hot magma ocean, water vapor and gasses escaped into the atmosphere. "It then rained out from the atmosphere as conditions got cool enough," said lead study author Benjamin Johnson, an assistant professor in the Department of Geological and Atmospheric Sciences at Iowa State University.

"We can't really say what the source of the water is from our work, but we do suggest that whatever the source, it was present when the magma ocean was still around," Johnson told Live Science in an email.

This pillow basalt lined the seafloor roughly 3.2 billion years ago.

This pillow basalt lined the seafloor roughly 3.2 billion years ago. (Image credit: Benjamin Johnson)

In the new study, Johnson and co-author Boswell Wing, an associate professor of geological sciences at the University of Colorado Boulder, turned to Panorama's unique landscape in the Australian outback. Its rocky scenery preserves a hydrothermal system dating to 3.2 billion years ago, "and records the entire ocean crust from the surface down to the heat engine that drove circulation," Johnson said. 

Preserved in that craggy seafloor were different versions, or isotopes, of oxygen; over time, the relationship between these isotopes can help scientists decode shifts in ancient ocean temperature and global climate.

However, the scientists uncovered something unexpected through their analysis of more than 100 sediment samples. They found that 3.2 billion years ago, oceans held more oxygen-18 than oxygen-16 (the latter is more common in the modern ocean). Their computer models showed that on a global scale, continental land masses leach oxygen-18 from the oceans. In the absence of continents, the oceans would carry more oxygen-18. And the ratio between these two oxygen isotopes hinted that at the time, there were no continents at all, the study found.

"This value is different than the modern ocean in a way that can be explained most easily by a lack of emergent continental crust," Johnson said in the email.

Other researchers have previously proposed the idea that Earth was once ocean covered, Johnson said. However, there's less agreement about how much of that crust was visible above sea level. This new discovery "provides actual geochemical constraints on the presence of land above sea level," he explained. 

The prospect of an ancient waterworld Earth also offers a new perspective on another intriguing question: where the planet's earliest forms of life appeared and how they evolved, the researchers wrote in the study.

"There are two major camps for the origin of life: hydrothermal vents and ponds on land," Johnson said. "If our work is accurate, it means the number of environments on land for life to emerge and evolve was really small or absent until sometime after 3.2 billion years ago."

The findings were published online today (March 2) in the journal Nature Geoscience.

Editor’s note: The headline of this article was updated on March 3 to correct the age of a continent-free Earth; while the evidence in this study dates to more than 3 billion years ago, Earth at that time was only 1.5 billion years old, not 3 billion years old.

Originally published on Live Science.

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Mindy Weisberger is an editor at Scholastic and a former Live Science channel editor and senior writer. She has reported on general science, covering climate change, paleontology, biology, and space. Mindy studied film at Columbia University; prior to Live Science she produced, wrote and directed media for the American Museum of Natural History in New York City. Her videos about dinosaurs, astrophysics, biodiversity and evolution appear in museums and science centers worldwide, earning awards such as the CINE Golden Eagle and the Communicator Award of Excellence. Her writing has also appeared in Scientific American, The Washington Post and How It Works Magazine.

  • Gordon Allen
    In the beginning, (beyond man's knowledge of time like eternity) God created the heavens and the earth. And the earth was (became) without form, and void; (because Lucifer, Satan) was cast into it. And darkness was upon the face of the deep. (because Satan had become darkness from rebelling against the light and truth of God in heaven who he had created to be the highest of archangels in heaven with tremendous glory above all the angels but he became envious of the most High God above him). He told the first lie to all the angels that he was above God himself and one third of the angels believed him rather than God which caused him and his fellow angels that believed him to lose their first estate forever and they all immediately fell as a stars from heaven into the core of the earth known as eternal hell, a place of darkness and an invisible fire to dwell in that is the hottest fire that is known to scientists that exists. And the invisible Spirit of God (Who is an invisible consuming fire) moved upon the face of the waters. And God said, "Let there be light." And it immediately came to pass and there was (became) light. And God called the light day. and the darkness he called night (to remind man that there is a vast difference between the darkness of Satan and the Light of God Almighty).
    Just read Genesis 1; Isaiah 14; and Revelation 12 in the Holy Bible and start believing the whole of it and you will be a different person when you come to know the grace of God through faith in His Word.
  • stanwagon
    The headline is wrong. Earth is 4.5 billion years old. So 3.2 billion years ago it was 1.3 billion years old, not 3 billion years old.
  • Bobism
    The Urantia Book explained this almost a 70 years ago. (almost 100 pre-publication)
  • Stoney51
    Well I'll be.
  • TorbjornLarsson
    admin said:
    Chemicals in ancient ocean rocks hint that 3.2 billion years ago, the surface of a baby Earth was continent-free and covered by a global ocean.

    3-billion-year-old Earth had water everywhere, but not one continent, study suggests : Read more

    This is neat in several respects. It gives a consistent continental area with older work. And it strengthens the recent result of life having evolved around ocean vents since life founding biochemical production happened there and in the same way as adopted in the first cells https://phys.org/news/2020-03-groundwork-life.html ].

    Their preferred model gives a very neat result of 3-5 % the current continental surface as "subaerial" (exposed to atmosphere), or ~ 0.7*4 = 2.8 % of the total surface area as continent at 3.2 Ga. This is a fair fit to older results that has the same general model resulting in "only 2–3% of the Earth's area consisted of emerged continental crust by around 2.5 Ga" combined with a very rapid increase hereafter https://www.sciencedirect.com/science/article/abs/pii/S0012821X08005748 ].

    The older paper has the continental crust mostly under magma and/or ocean due to it being thinner with the then hotter mantle. The quick subaerial rise is suggested to explain the quick change from CO2 to O2 dominated atmosphere due to several changes in erosion gas sinks.
  • TorbjornLarsson
    Gordon Allen said:
    In the beginning, (beyond man's knowledge of time

    Could you take your evangelizing erroneous superstition somewhere else than on science sites? For instance, we do know cosmological time at 0.15 % uncertainty, while suoerstition know nothing or false (as here).
  • TorbjornLarsson
    Bobism said:
    The Urantia Book explained this almost a 70 years ago. (almost 100 pre-publication)

    It's myth - that explains exactly nothing, by default.
  • erock
    In the beginning God created the heaven and the earth.
    2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the watersSo now they are getting somewhere, science always seems to come around to creation...
  • erock
    and before someone snake bites me: Not evangelizing, just sayin:) You choose:)
  • Broadlands
    There are 3.7 billion year-old sedimentary rocks with evidence of life, stromatolites with cyanobacteria releasing free oxygen. They occur in Greenland, not in Western Australia.