Evidence from an ancient section of the Earth’s crust suggest that Earth was once a water-world, some three billion years ago. If true, it’ll mean scientists need to reconsider some thinking around exoplanets and habitability. They’ll also need to reconsider their understanding of how life began on our planet.
The work is focused on an area in the Australian Outback called the Panorama district. In that region in northwestern Australia there’s a slab of ocean floor 3.2 billion years old, that’s been turned on its side. The chunk of crust holds chemical clues about ancient Earth’s seawater.
“There are no samples of really ancient ocean water lying around, but we do have rocks that interacted with that seawater and remembered that interaction,” Johnson said in a press release.
“The origin and evolution of Earth’s biosphere were shaped by the physical and chemical histories of the oceans.”
From the paper “Limited Archaean continental emergence reflected in an early Archaean 18O-enriched ocean.
The authors wanted to re-boot the debate over what ancient Earth looked like, and to break new ground in the discussion.
In the introduction to their paper, the two authors say “The origin and evolution of Earth’s biosphere were shaped by the physical and chemical histories of the oceans. Marine chemical sediments and altered oceanic crust preserve a geochemical record of these histories. Marine chemical sediments, for example, exhibit an increase in their 18O/16O ratio through time.”
Marine sediments have been well-studied over time, but the authors of this study looked at the ancient crust instead. The ancient oceans held different types of oxygen that were then deposited into the crust. The scientists gathered over 100 samples of the ancient rock and analyzed it for two oxygen isotopes: oxygen-16 and oxygen 18. They wanted to find the relative amount of each isotope in the ancient crust, to compare it to the amounts in the sediment.
Artist impression of the early Earth. Credit: NASA Goddard Space Flight Center Conceptual Image Lab
Their results showed more oxygen-18 in the crust when it was formed 3.2 billion years ago, meaning the ocean at that time had more oxygen-18. The pair of researchers say that means that when that crust formed, there were no continents. This is because when continents form, they contain clays, and those clays would have absorbed the heavier oxygen-18. So if there had been continents 3.2 billion years ago, their crust samples would have held less oxygen-18.
The over-arching conclusion of their work is that the Earth’s oceans went through two distinct states: one prior to continents forming, and one after continents formed.
Marine chemical sediments have been studied extensively to try to piece together continent formation on ancient Earth. As the study says, those ancient sediments include “carbonates, phosphates, microcrystalline silica and iron oxides. As these minerals form directly from aqueous species, they can reflect the ?18O of the water with which they coexist.” The sediments are like an archival record of Earth at the time, and the older sediments show oxygen-18 values increasing steadily through time, all the way up to today. But this work contrasts with that, and the authors suggest that seawater oxygen-18 decreased through time.
Artist’s depiction of a watery exoplanet orbiting a distant red dwarf star. New research indicates that Proxima b could be especially watery. Credit: CfA
The pair of scientists constructed a model for ancient Earth, showing that “the initiation of continental weathering in the late Archaean, between 3 and 2.5 billion years ago, would have drawn down an 18O-enriched early Archaean ocean to ?18O values similar to those of modern seawater.” So only after continents formed, could the oxygen-18 values begin to look like modern values.
Although this study points to the possibility of ancient Earth as a water-world, it doesn’t mean that the planet was without any land-forms. Island-size areas of land, or even micro-continents, may have existed at the time, volcanic in nature, and very rocky. But the types of vast land-forms that cover the Earth today, rich in soil and with tall mountain ranges, may not have existed. If they had, the oxygen-18 content would have more closely resembled today’s.
“There’s nothing in what we’ve done that says you can’t have teeny, micro-continents sticking out of the oceans,” Wing said in a press release. “We just don’t think that there were global-scale formation of continental soils like we have today.”
The authors aren’t suggesting that their work is the definitive piece of evidence in the ongoing discussion around early Earth. They note that their are other possible reasons for their results.
If the ancient continents formed much more slowly than modern continents, that could explain the the discrepancy in oxygen-18. It’s also possible that the clays that absorb oxygen-18 formed in the ocean itself, rather than on the continents.
That points to an enduring mystery in Earth science: when exactly did continents form?
Gondwana 420 million years ago. Image Credit: By Fama Clamosa – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=67001070
It’s likely, according to some evidence, that the continents could only form as the Earth’s core shed heat and cooled down. In any case, modern continents didn’t take shape until after the Jurassic. Prior to that, the single super-continent of Gondwana covered about one-fifth of the Earth’s surface. Wing wants to examine younger areas of the Earth’s crust to try to determine more clearly when the modern continents formed.
This study also touches on early life on Earth, and how and when it formed. Earth’s early oceans, much like modern oceans, acted as a buffer, which “mediated climatic feedbacks between the biosphere, atmosphere and geosphere through deep time, helping to ensure long-term planetary habitability.”
In this illustration, the exoplanet GJ 1214 b, a likely ocean world, is shown between Earth and Neptune for comparison. Image Credit: By Aldaron, a.k.a. Aldaron – Own work, incorporating public domain images for reference planets (see below), inspired by Thingg’s size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8854174
Science has painted a picture of what the early Earth may have looked like, and what the nature of the oceans was. But it’s far from complete. The evidence is all buried, in rock and in time. And as we seek to understand climate change here on Earth, and as we get better and better looks at exoplanets, all these questions about ancient Earth, the oceans, and the biosphere, take on new importance.
As the authors say in their paper, “An early Earth without emergent continents may have resembled a ‘water world’, providing an important environmental constraint on the origin and evolution of life on Earth as well as its possible existence elsewhere.“
“The history of life on Earth tracks available niches,” said Wing. “If you’ve got a waterworld, a world covered by ocean, then dry niches are just not going to be available.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
