How did life survive 'Snowball Earth'? In ponds, study suggests
Earth has not always been so hospitable to live. During several ice ages, the planet's surface was almost completely frozen over, creating what has been dubbed "Snowball Earth".
Liquid water appears to be the most important ingredient for life on any planet, raising the question: how did anything survive such frosty, brutal times?
A group of scientists said Thursday that they had found an astonishing diversity of micro-organisms in tiny pools of melted ice in Antarctica, suggesting that life could have ridden out Snowball Earth in similar ponds.
During the Cryogenian Period between 635 and 720 million years ago, the average global temperature did not rise above -50 degrees Celsius (-58 Fahrenheit). The climate near the equator at the time resembled modern-day Antarctica.
Yet even in such extreme conditions, life found a way to keep evolving.
Fatima Husain, the lead author of a new study published in Nature Communications, told AFP there was evidence of complex life forms "before and after the Cryogenian in the fossil record".
"There are multiple hypotheses regarding possible places life may have persisted," said Husain, a graduate student at the Massachusetts Institute of Technology.
Perhaps it found shelter in patches of open ocean, or in deep-sea hydrothermal vents, or under vast sheets of ice.
The tiny melted ice pools that dotted the equator were another proposed refuge.
These ponds could have been oases for eukaryotes, complex organisms that eventually evolved into multicellular life forms that would rise to dominate Earth, including humans.
- Could aliens be hiding in ponds? -
Melted ice ponds still exist today in Antarctica, at the edges of ice sheets.
In 2018, members of a New Zealand research team visited the McMurdo ice shelf in east Antarctica, home to several such pools, which are only a few metres wide and less a metre deep.
The bottom of the ponds are lined with a mat of microbes that have accumulated over the years to form slimy layers.
"These mats can be a few centimetres thick, colourful, and they can be very clearly layered," Husain said.
They are made up of single-celled organisms called cyanobacteria that are known to be able to survive extreme conditions.
But the researchers also found signs indicating there were eukaryotes such as algae or microscopic animals.
This suggests there was surprising diversity in the ponds, which appears to have been influenced by the amount of salt each contained.
"No two ponds were alike," Husain said. "We found diverse assemblages of eukaryotes from all the major groups in all the ponds studied."
"They demonstrate that these unique environments are capable of sheltering diverse assemblages of life, even in close proximity," she added.
This could have implications in the search for extraterrestrial life.
"Studies of life within these special environments on Earth can help inform our understanding of potential habitable environments on icy worlds, including icy moons in our Solar System," Husain said.
Saturn's moon Enceladus and Jupiter's Europa are covered in ice, but scientists increasingly suspect they could be home to simple forms of life, and several space missions have been launched to find out more about them.
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CNN
27 minutes ago
- CNN
A hunt for ghostly particles found strange signals coming from Antarctic ice. Scientists are still trying to explain them
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USA Today
3 hours ago
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What happens when you use ChatGPT to write an essay? See what new study found.
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Forbes
4 hours ago
- Forbes
How Life Survived Snowball Earth
Artist's impression of "Snowball Earth." The Snowball Earth hypothesis suggests that, hundreds of ... More millions of years ago, the Earth's surface may have frozen solid as a result of severe climate change. During the Cryogenian period about 700 to 635 million years ago, Earth experienced a super ice age, one that froze the entire planet from the poles to the equator. Scientist have long wondered how life survived this 'Snowball Earth.' Most of the surface was covered by ice, so there was no to little sunlight reaching the oceans, and with no weathering happening on the frozen-solid continents, no nutrients were washed into the sea. Maybe hot springs deep beneath the ice provided a last viable spot where life persisted until the ice receded. In a new study, researchers at MIT's Department of Earth, Atmospheric and Planetary Sciences, the Natural History Museum in London and the University of Waikato in New Zealand, propose an alternative hypothesis. 'We're interested in understanding the foundations of complex life on Earth. We see evidence for eukaryotes before and after the Cryogenian in the fossil record, but we largely lack direct evidence of where they may have lived during,' says lead author Fatima Husain, a graduate student in MIT. 'The great part of this mystery is, we know life survived. We're just trying to understand how and where.' The scientists found that lifeforms could have survived the global freeze by living in watery oases on the surface. Similar environmental conditions still exist today in cryoconite holes. Dark-colored dust and debris transported by glaciers to the surface absorb sunlight, heating up and melting into the ice forming small pockets and holes. At temperatures hovering around 0 degrees Celsius, the resulting meltwater ponds could have served as habitable environments for early life. Cryoconite hole on a glacier The researchers analyzed samples from a variety of cryoconite holes and meltwater ponds located on the McMurdo Ice Shelf in an area that was first described by members of Robert Falcon Scott's 1903 expedition as 'dirty ice.' They discovered clear signatures of life in every pond. Even more surprising, the communities varied from pond to pond, revealing a high diversity of life forms. There were cyanobacteria, prokaryotic, single-celled photosynthetic organisms that lack a cell nucleus or other organelles. The oldest cyanobacteria-like fossils appear on Earth over 3 billion years ago. While these ancient microbes are known to survive within some of the the harshest environments on Earth, the researchers wanted to know whether eukaryotes — complex organisms that evolved a cell nucleus and other membrane bound organelles — could also weather similarly challenging circumstances. Chemical analysis showed the presence of various molecules clearly associated with eukaryotic life. The team found that salinity plays a key role in the kind of life a pond can host: Ponds that were more brackish or salty had more similar communities, which differed from those in ponds with fresher waters. 'No two ponds were alike,' Husain explains. 'There are repeating casts of characters, but they're present in different abundances. And we found diverse assemblages of eukaryotes from all the major groups in all the ponds studied. These eukaryotes are the descendants of the eukaryotes that survived the Snowball Earth. This really highlights that meltwater ponds during Snowball Earth could have served as above-ice oases that nurtured the eukaryotic life that enabled the diversification and proliferation of complex life — including us — later on.' Additional material and interviews provided by MIT News.
