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Earth’s earliest forest revealed in Somerset fossils

Thu, 07/03/2024 - 10:27

The oldest fossilised forest known on Earth – dating from 390 million years ago – has been found in the high sandstone cliffs along the Devon and Somerset coast of South West England.

Ice cores provide first documentation of rapid Antarctic ice loss in the past

Thu, 08/02/2024 - 10:00

The evidence, contained within an ice core, shows that in one location the ice sheet thinned by 450 metres — that’s more than the height of the Empire State Building — in just under 200 years.

This is the first evidence anywhere in Antarctica for such a fast loss of ice. Scientists are worried that today’s rising temperatures might destabilize parts of the West Antarctic Ice Sheet in the future, potentially passing a tipping point and inducing a runaway collapse. The study, published in Nature Geoscience, sheds light on how quickly Antarctic ice could melt if temperatures continue to soar.

“We now have direct evidence that this ice sheet suffered rapid ice loss in the past,” said Professor Eric Wolff, senior author of the new study from Cambridge’s Department of Earth Sciences. “This scenario isn’t something that exists only in our model predictions and it could happen again if parts of this ice sheet become unstable.”

From west to east, the Antarctic ice sheets contain enough freshwater to raise global sea levels by around 57 metres. The West Antarctic Ice Sheet is considered particularly vulnerable because much of it sits on bedrock below sea level.

Model predictions suggest that a large part of the West Antarctic Ice Sheet could disappear in the next few centuries, causing sea levels to rise. Exactly when and how quickly the ice could be lost is, however, uncertain.

One way to train ice sheet models to make better predictions is to feed them with data on ice loss from periods of warming in Earth’s history. At the peak of the Last Ice Age 20,000 years ago, Antarctic ice covered a larger area than today. As our planet thawed and temperatures slowly climbed, the West Antarctic Ice Sheet contracted to more or less its current extent.

“We wanted to know what happened to the West Antarctic Ice Sheet at the end of the Last Ice Age, when temperatures on Earth were rising, albeit at a slower rate than current anthropogenic warming,” said Dr Isobel Rowell, study co-author from the British Antarctic Survey. “Using ice cores we can go back to that time and estimate the ice sheet’s thickness and extent.”

Ice cores are made up of layers of ice that formed as snow fell and was then buried and compacted into ice crystals over thousands of years. Trapped within each ice layer are bubbles of ancient air and contaminants that mixed with each year’s snowfall — providing clues as to the changing climate and ice extent.

The researchers drilled a 651-metre-long ice core from Skytrain Ice Rise in 2019. This mound of ice sits at the edge of the ice sheet, near the point where grounded ice flows into the floating Ronne Ice Shelf.

After transporting the ice cores to Cambridge at -20C, the researchers analysed them to reconstruct the ice thickness. First, they measured stable water isotopes, which indicate the temperature at the time the snow fell. Temperature decreases at higher altitudes (think of cold mountain air), so they could equate warmer temperatures with lower-lying, thinner ice.

They also measured the pressure of air bubbles trapped in the ice. Like temperature, air pressure also varies systematically with elevation. Lower-lying, thinner ice contains higher-pressure air bubbles.

These measurements told them that ice thinned rapidly 8,000 years ago. “Once the ice thinned, it shrunk really fast,” said Wolff, “this was clearly a tipping point — a runaway process.”

They think this thinning was probably triggered by warm water getting underneath the edge of the West Antarctic Ice Sheet, which normally sits on bedrock. This likely untethered a section of the ice from bedrock, allowing it to float suddenly and forming what is now the Ronne Ice Shelf. This allowed neighbouring Skytrain Ice Rise, no longer restrained by grounded ice, to thin rapidly. 

The researchers also found that the sodium content of the ice (originating from salt in sea spray) increased about 300 years after the ice thinned. This told them that, after the ice thinned, the ice shelf shrunk back so that the sea was hundreds of kilometres nearer to their site.

“We already knew from models that the ice thinned around this time, but the date of this was uncertain,” said Rowell. Ice sheet models placed the retreat anywhere between 12,000 and 5,000 years ago and couldn’t say how quickly it happened. “We now have a very precisely dated observation of that retreat that can be built into improved models,” said Rowell.

Although the West Antarctic Ice Sheet retreated quickly 8,000 years ago, it stabilised when it reached roughly its current extent. “It’s now crucial to find out whether extra warmth could destabilise the ice and cause it to start retreating again,” said Wolff.

Reference:
Grieman et al. (2024) Abrupt Holocene ice loss due to thinning and ungrounding in the Weddell Sea Embayment. Nature Geoscience. DOI: 10.1038/s41561-024-01375-8

Researchers from the University of Cambridge and the British Antarctic Survey have uncovered the first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically at the end of the Last Ice Age, around 8,000 years ago.

University of Cambridge / British Antarctic SurveyTents at Skytrain Ice Rise


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Ancient seafloor vents spewed tiny, life-giving minerals into Earth’s early oceans

Fri, 02/02/2024 - 16:38

Their study, published in Science Advances, examined 3.5-billion-year-old rocks from western Australia in previously unseen detail and identified large quantities of a mineral called greenalite, which is thought to have played a role in early biological processes. The researchers also found that the seafloor vents would have seeded the oceans with apatite, a mineral rich in the life-essential element phosphorus.

The earliest lifeforms we know of—single-celled microorganisms, or microbes—emerged around 3.7 billion years ago. Most of the rocks that contain traces of them and the environment they lived in have, however, been destroyed. Some of the only evidence we have of this pivotal time comes from an outcrop of sediments in the remote Australian outback.

The so-called Dresser Formation has been studied for years but, in the new study, researchers re-examined the rocks in closer detail, using high magnification electron microscopes to reveal tiny minerals that were essentially hidden in plain sight.

The greenalite particles they observed measured just a few hundred nanometres in size—so small that they would have been washed over thousands of kilometres, potentially finding their way into a range of environments where they may have kick-started otherwise unfavourable chemical reactions, such as those involved in building the first DNA and RNA molecules.

“We’ve found that hydrothermal vents supplied trillions upon trillions of tiny, highly-reactive greenalite particles, as well as large quantities of phosphorus,” said Professor Birger Rasmussen, lead author of the study from the University of Western Australia.

Rasmussen said scientists are still unsure as to the exact role of greenalite in building primitive cells, “but this mineral was in the right place at the right time, and also had the right size and crystal structure to promote the assembly of early cells.”

The rocks the researchers studied contain characteristic layers of rusty-red, iron-rich jasper which formed as mineral-laden seawater spewed from hydrothermal vents. Scientists had thought the jaspers got their distinctive red colour from particles of iron oxide which, just like rust, form when iron is exposed to oxygen.

But how did this iron oxide form when Earth’s early oceans lacked oxygen? One theory is that photosynthesising cyanobacteria in the oceans produced the oxygen, and that it wasn’t until later, around 2.4 billion years ago, that this oxygen started to skyrocket in the atmosphere.

The new results change that assumption, however, “the story is completely different once you look closely enough,” said study co-author Professor Nick Tosca from Cambridge’s Department of Earth Sciences.

The researchers found that tiny, drab, particles of greenalite far outnumbered the iron oxide particles which give the jaspers their colour. The iron oxide was not an original feature, discounting the theory that they were formed by the activity of cyanobacteria.

“Our findings show that iron wasn’t oxidised in the oceans; instead, it combined with silica to form tiny crystals of greenalite,” said Tosca. “That means major oxygen producers, cyanobacteria, may have evolved later, potentially coinciding with the soar in atmospheric oxygen during the Great Oxygenation Event.”

Birger said that more experiments are needed to identify how greenalite might facilitate prebiotic chemistry, “but it was present in such vast quantities that, under the right conditions its surfaces could have synthesized an enormous number of RNA-type sequences, addressing a key question in origin of life research – where did all the RNA come from?” 

Reference:
Rasmussen, B., Muhling, J., Tosca, N.J. 'Nanoparticulate apatite and greenalite in oldest, well-preserved hydrothermal vent precipitates.' Science Advances (2024). DOI: 10.1126/sciadv.adj4789

Researchers from the universities of Cambridge and Western Australia have uncovered the importance of hydrothermal vents, similar to underwater geysers, in supplying minerals that may have been a key ingredient in the emergence of early life.

MARUM − Zentrum für Marine Umweltwissenschaften, Universität BremenThe hydrothermal vent "Candelabra" in the Logatchev hydrothermal field on the Mid-Atlantic Ridge at a water depth of 3300 m


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Mysterious missing component in the clouds of Venus revealed

Tue, 09/01/2024 - 10:05

What are the clouds of Venus made of? Scientists know they are mainly made of sulfuric acid droplets, with some water, chlorine, and iron. Their concentrations vary with height in the thick and hostile Venusian atmosphere. But until now they have been unable to identify the missing component that would explain the clouds’ patches and streaks, only visible in the UV range.

In a study published in Science Advances, researchers from the University of Cambridge synthesised iron-bearing sulfate minerals that are stable under the harsh chemical conditions in the Venusian clouds. Spectroscopic analysis revealed that a combination of two minerals, rhomboclase and acid ferric sulfate, can explain the mysterious UV absorption feature on our neighbouring planet.

“The only available data for the composition of the clouds were collected by probes and revealed strange properties of the clouds that so far we have been unable to fully explain,” said Paul Rimmer from the Cavendish Laboratory and co-author of the study. “In particular, when examined under UV light, the Venusian clouds featured a specific UV absorption pattern. What elements, compounds, or minerals are responsible for such observation?”

Formulated on the basis of Venusian atmospheric chemistry, the team synthesised several iron-bearing sulfate minerals in an aqueous geochemistry laboratory in the Department of Earth Sciences. By suspending the synthesised materials in varying concentrations of sulfuric acid and monitor the chemical and mineralogical changes, the team narrowed down the candidate minerals to rhomboclase and acid ferric sulfate, of which the spectroscopic features were examined under light sources specifically designed to mimic the spectrum of solar flares (Rimmer’s FlareLab; Cavendish Laboratory).

Researchers from Harvard University provided measurements of the UV absorbance patterns of ferric iron under extreme acidic conditions, in an attempt to mimic the even more extreme Venusian clouds. The scientists are part of the newly-established Origins Federation, which promotes such collaborative projects.

“The patterns and level of absorption shown by the combination of these two mineral phases are consistent with the dark UV-patches observed in Venusian clouds,” said co-author Clancy Zhijian Jiang, from the Department of Earth Sciences, Cambridge. “These targeted experiments revealed the intricate chemical network within the atmosphere, and shed light on the elemental cycling on the Venusian surface.”

“Venus is our nearest neighbour, but it remains a mystery,” said Rimmer. “We will have a chance to learn much more about this planet in the coming years with future NASA and ESA missions set to explore its atmosphere, clouds and surface. This study prepares the grounds for these future explorations.”

The research was supported by the Simons Foundation, and the Origins Federation.

Reference:
Clancy Zhijian Jiang et al., ‘Iron-sulfur chemistry can explain the ultraviolet absorber in the clouds of Venus.’ Science Advances (2024). DOI:10.1126/sciadv.adg8826

Researchers may have identified the missing component in the chemistry of the Venusian clouds that would explain their colour and 'splotchiness' in the UV range, solving a longstanding mystery.

FreelanceImages/Universal Images Group/Science Photo Library via Getty ImagesSunrise over Venus


The text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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