Macquarie University research shows a chemical banned in Europe but still sprayed on Australian produce to kill fungus also wipes out beneficial insects and pollinators, potentially fuelling global insect decline.
A widely-used agricultural chemical sprayed on fruits and vegetables to prevent fungal disease is also killing beneficial insects that play a critical role in pollination and wider ecosystems.
New Macquarie University-led research published in Royal Society Open Science, shows chlorothalonil, one of the world’s most widely used agricultural fungicides, deeply impacts the reproduction and survival of insects, even at the lowest levels routinely found on food from cranberries to wine grapes.
“Even the very lowest concentration has a huge impact on the reproduction of the flies that we tested,” says lead author, PhD candidate Darshika Dissawa, from Macquarie’s School of Natural Sciences.
“This can have a big knock-on population impact over time because it affects both male and female fertility.”
The insect species Drosophila melanogaster, commonly called fruit fly or vinegar fly, was used as a laboratory model representing countless non-target insects found in agricultural environments.
“D. melanogaster is also at the bottom of the food chain, becoming food for a whole lot of other species,” says Dissawa.
Unlike major horticultural pests in Australia, such as the Queensland fruit fly (Bactrocera tryoni) and the Mediterranean fruit fly (Ceratitis capitata), D. melanogaster feed on rotting fruit and play an important role in nutrient recycling in agriculture.
Testing the fungicide
Scientists exposed D. melanogaster larvae to chlorothalonil amounts matching levels typically found in fruits and vegetables.
Even at the lowest dose tested, the flies showed a 37 per cent drop in egg production at their maturity, compared with unexposed individuals.
Supervising author Associate Professor Fleur Ponton, from Macquarie’s School of Natural Sciences, says the dramatic decline was surprising.
“We expected the effect to increase far more gradually with higher amounts. But we found that even a very small amount can have a strong negative effect,” Associate Professor Ponton says.
The findings add to mounting evidence of what researchers call the “insect apocalypse” – a global phenomenon that has seen insect populations plummet by more than 75 per cent in some regions in recent decades.
Where the fungicide is used
Although banned in the European Union, chlorothalonil is extensively applied to Australian crops to control fungal diseases such as mildews and leaf blights.
The chemical has been detected in soil and water bodies near agricultural areas, with residue levels in fruits and vegetables ranging from trace amounts to 460 milligrams per kilogram.
“Chlorothalonil is particularly common in orchards and vineyards and is often used preventatively when no disease is present,” Associate Professor Ponton explains.
“People assume fungicides like chlorothalonil only impact fungal diseases, but they can have devastating, unintended consequences for other species.” says Associate Professor Ponton.
Knock-on effect
The study found that chlorothalonil exposure during larval development caused severe reproductive damage in adult flies.
Females showed significantly reduced body weight, fewer egg-producing structures called ovarioles and drastically reduced egg production. Males had reduced iron levels, suggesting disruption to metabolic processes essential for sperm production.
The scientists also found the larvae consumed the contaminated food normally, ruling out taste aversion as an explanation.
“We didn’t find a significant aversion for food contaminated with chlorothalonil, except when there was a very high concentration of the chemical,” says Associate Professor Ponton. “This means the impacts are due to chlorothalonil ingestion.”
Knowledge gap has broad implications
In agricultural landscapes where entire orchards and vineyards are treated with fungicides, insects cannot escape chemically-contaminated food sources.
“We need bees and flies and other beneficial insects for pollination, and we think this is an important problem for pollinator populations,” Associate Professor Ponton says. “There is a strong commercial incentive to understand the impact in the field and address the use of this chemical.”
The research highlights a critical knowledge gap in pesticide regulation. Chlorothalonil is one of the most extensively used fungicides globally, but fewer than 25 scientific papers examine its effects on insects, despite mounting evidence of widespread insect population decline.
“People assume fungicide only affects fungal diseases, but it has an effect on other non-target organisms,” Associate Professor Ponton says.
The researchers have called for more sustainable agricultural practices, such as reduced frequency of applications to allow insect populations to recover between treatments.
“We need field trials to explore options and develop evidence-based guidelines to consider the knock-on effects of fungicides on beneficial insects,” says Associate Professor Ponton.
Future research will examine whether the reproductive damage carries over to subsequent generations and investigate the combined effects of multiple agricultural chemicals typically used together in farming operations.
Reference: Dissawa MD, Boyer I, Ponton F. Chlorothalonil exposure impacts larval development and adult reproductive performance in Drosophila melanogaster. Royal Soc Open Sci. 2025. doi: 10.1098/rsos.250136
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The Earth’s atmosphere is now trapping far more heat than climate models predicted. This energy imbalance has doubled since 2005, from 0.6 to 1.3 watts per square meter, according to researchers from Australia, France and Sweden. The Conversation reports.
Scientists believe the acceleration is due to the accumulation of greenhouse gases and changes in cloud cover. In particular, the area of white reflective clouds has decreased, while darker ones have increased. This weakens the planet’s ability to reflect the sun’s heat back into space.
Most of the additional energy (up to 90%) is absorbed by the oceans, but there is also melting of glaciers and warming of land. This accumulation of heat has alreadyraised the average temperatureof the Earth by 1.3–1.5°C compared to the pre-industrial period.
The authors emphasize that real changes are happening faster than the models predict. If the trend continues, the world could face increased heat waves, droughts and storms. What is particularly worrying is that only models with high sensitivity to emissions come close to the recorded values – they predict more severe warming in the future.
An additional threat is a possible reduction in funding for satellite climate monitoring in the United States, a key tool that allows us to capture such changes at an early stage.
Ecosystems aren’t just defined by what species exist, but by how much life they contain. While scientists understand species diversity and where marine life is most abundant today, we still lack a clear picture of how biomass, the total weight of living organisms, has changed over time.
Biomass reveals the real impact and energy flow of life in an ecosystem, like knowing not just the cast of a play, but who the lead actors are and how powerful their performances can be. It’s a vital clue to understanding an ecosystem’s true strength and health across deep time.
While scientists have long known that biodiversity has increased throughout Earth’s history, a new Stanford study adds a key piece: biomass, or the total amount of ocean life, has also mostly grown over the last 500 million years.
Despite some dips during mass extinction events, the overall trend is upward, just like biodiversity. This suggests a powerful link: as life became more diverse, it also became more abundant, filling the oceans with both variety and volume.
Scientists uncover massive, diverse ecosystem deep beneath Earth’s surface
Imagine if ancient seas left behind a diary, not in words, but in shells and skeletons. That’s exactly what the team is decoding. Researchers studied thousands of rock samples packed with the fossilized remains of marine organisms, shells, algae, and tiny protists. These fossils recorded the biomass of their time, that is, the total “living material” preserved across Earth’s history.
Why does it matter?
Biomass reveals how much life an ecosystem could support, and how much energy it moves around, making it a key sign of past ocean health.
Although it once seemed too complex to measure across deep time, researchers took on the challenge. They analyzed over 7,700 limestone samples spanning 540 million years, using a method called petrographic point-counting to examine the amount of fossilized shell material.
By combining decades of studies with new data, they created a clearer picture of how life in Earth’s oceans has ebbed and flowed through deep history.
Some sea life could face extinction over the next century
They found that in the Cambrian Period, fewer than 10% of rocks had shell material. As life diversified during the Ordovician, that percentage rose, evidence of the Cambrian Explosion.
Calcifying sponges were among the early biomass leaders but were soon overtaken by echinoderms (like early starfish) and marine arthropods (like trilobites and crab ancestors).
Over the past 230 million years, oceans saw dramatic rises and falls in life, recorded in the shell content of marine rocks. Shell material stayed above 20%, signaling healthy ocean life, until the Late Devonian extinction (~375–360 million years ago) caused a notable drop.
Then came the worst: the Great Dying (~250 million years ago), the Permian-Triassic extinction, when shell content plunged to just 3%, reflecting a massive collapse in marine life.
Even after major extinctions like the end-Triassic and the one that ended the dinosaurs, marine life bounced back. In today’s era, the Cenozoic, shell remains now make up over 40% of marine rocks, largely due to mollusks and corals thriving.
To be sure, this rise reflected real increases in ocean life, not just fewer shell-destroying predators or sampling bias, researchers ran thorough tests. They analyzed fossil samples across shallow and deep waters, various latitudes, and different ancient continental setups.
Animal poop helps ecosystems adapt to climate change, study
The result? The trend held strong across the board, showing that the growth in shell content truly reflects a long-term rise in ocean biomass.
As ocean organisms became more specialized, they got better at using energy and nutrients, boosting ecosystem productivity. This efficient recycling from phytoplankton to decomposers helped support more life, reflected in greater biomass.
But today, human impacts like pollution, overfishing, and climate change threaten that balance. Scientists warn we may be entering a sixth mass extinction, where shrinking biodiversity could reduce biomass, and future fossil records might carry the traces of this decline.
Jonathan Payne, Dorrell William Kirby Professor of Earth and Planetary Sciences, said, “Our findings show that overall biomass is linked to biodiversity and that losses in biodiversity may suppress productivity for geologically meaningful intervals, adding one more argument for why conserving biodiversity is essential for the health of humans and our planet.”
Journal Reference:
Pulkit Singh, Jordan Ferré, Bridget Thrasher, et al. Macroevolutionary coupling of marine biomass and biodiversity across the Phanerozoic. Current Biology. DOI: 10.1016/j.cub.2025.06.006
I caught a glimpse of the satellite as it flew over Ireland, just weeks before it bursts into flames.
Nearly two years after being launched into space, Ireland’s very first satellite mission is about to come to a close.
Throughout its lifespan, the tiny cuboid satellite, called EIRSAT-1, sent down troves of data to ground control at University College Dublin (UCD), sharing what it found about the secrets of the universe, while setting up the precedence for more student-led Irish space projects to come.
Recently, SiliconRepublic.com visited mission control at UCD – a small office laden with computers – to meet with the team behind the project.
“It’s the first Irish satellite and something that we’re very, very proud of,” says Dr David Murphy, the satellite’s systems engineer and a research fellow at the UCD C-Space, Centre for Space Research.
The EIRSAT-1, or Education Research Satellite-1’s story began back in 2017 through the European Space Agency’s (ESA) Fly Your Satellite! program.
The UCD-led project received support from Queen’s University Belfast and a number of Irish space tech companies.
In its time, the satellite detected nearly a dozen gamma ray bursts and a few solar flares, and the team tells SiliconRepublic.com that they are already developing newer projects that build on what they learnt from this small – yet large – leap into Ireland’s achievements in space science.
Late last week, UCD announced another ESA-funded space project which is set to send a swarm of satellites to the Earth’s orbit to detect more gamma ray bursts. Murphy has been working on this new project, called Comcube-S, for a while now.
The making of
Over the years, more than 60 people, comprising of students and early-career researchers, helped create EIRSAT-1. At its tail end, the project has about 10 active contributors.
Nearly six years of development went into building and testing the EIRSAT-1, including several months where the team had to work remotely as a result of the Covid-19 pandemic.
They received support from various government agencies through grants, as well as through Prodex, an ESA programme that supports university space projects.
Using this, they were able to fund their research, test the spacecraft and provide scholarships for their contributors.
However, after some unavoidable legislative setbacks and launch delays later, the satellite finally took to space in late 2023 on the ESA’s Vega-C rocket.
EIRSAT-1. Image: ESA
The EIRSAT-1 has a length and width of about 10.6cm and a height of 22.7cm. Inside its small aluminium body, the spacecraft is fitted with parts that help navigate and orient itself and collect data and send it back down to Earth.
A few of these complex parts include a magnet worker that lines the satellite to Earth’s magnetic field, a “very, very cool” antenna deployment mechanism, as pointed out to me by Murphy, a gamma ray detector and a sun sensor, which shows the accurate angle between the sun and the spacecraft.
The satellite is covered on all sides with solar panels. Some of its body is anodized – or coated with a protective oxide layer – which ensures that the aluminium parts do not cold weld with parts of the rocket.
Using this tiny complicated box floating alone in space, the scientists at UCD were able to detect around a dozen gamma rays – up from two when I last spoke to Murphy near Christmas last year. They also detected two solar flares.
“[Gamma rays] are the most luminous explosions in the universe,” Caimin McKenna, a current PhD student in the Space Science Group at UCD tells me. These rays are produced by the hottest and most energetic objects in the universe such as neutron stars and supernova explosions.
McKenna, 25, was pursuing his undergraduate degree when calls were put out for students to join the EIRSAT-1 programme.
Although, after the first few successful sightings, gamma ray detection “turned into work”, the team told me, laughing. Still, they were excited for more.
Interception
Our conversation was briefly diverted when the EIRSAT-1 neared Ireland overhead at around 12:40 pm that afternoon.
Each day, the satellite sends data it collects while flying over the country via two on-ground communication systems – one above the UCD building we were at, and one in a goat farm in Co Kerry.
The small control room is fitted with several computers. On one monitor, I could see the tiny satellite approaching Ireland, while on a larger one on the wall, I could see faint red bands, which got darker and more prominent as the satellite neared us.
EIRSAT-1 control room, UCD. Image: Suhasini Srinivasaragavan
The two-way communication happens through amateur radio frequency bands. The team sends audio tones to the spacecraft, which it can decode into commands, sending back the requested data.
“Essentially, it’s sending beeps and boops,” Murphy tells me. The beeps and boops contain troves of scientific data. “It’s like a constant stream of data down from the spacecraft to us.” The EIRSAT has made hundreds of such rounds.
However, less than two years after being thrusted into space on a rocket, this tiny spacecraft wandering the Earth’s orbit is set to burn up in the atmosphere. “It’s essentially spiralling down to Earth”, Murphy tells me. “We’ve got weeks left now”.
“It’s sad on one side that you know, it’s burning up and it’s only been about a year and a half since we launched,” Dr Joe Thompson, the project’s chief engineer tells me.
“But on the other side, we have to be very happy with how successful it all was. It’s surpassed all of our expectations.”
Although, the team isn’t entirely sure when the satellite will burn up. “At some point, I think a bunch of people are just going to be sitting around in the room wondering ‘Is this the last time we talked to her?’,” Thompson says.
While the team is sad to see “her” go, they tell me that they’ll do something to commemorate the journey and its end.
All Ways Home
The EIRSAT-1 story isn’t just a victory for the dozens who developed and launched the spacecraft. It’s a win for the wide-eyed ones among us who stare up at the sky wondering what it all means.
It’s a win for Ireland, which has showcased the calibre of its academic prowess, creating the precedence for a potential space program of its own one day – hopefully.
It also gave bragging rights to Thompson’s nephew who told his class that “uncle joe” went to California to launch a rocket.
Although the brains behind the project were sitting at UCD, EIRSAT-1 received support from school children across the country who poured their creativity to design special mission patches.
A few design submissions for the EIRSAT-1 mission patches. Image: Suhasini Srinivasaragavan
12 DEIS secondary school students, along with contributors from UCD, also wrote a poem, entitled ‘All Ways Home’ which is etched onto the side of EIRSAT-1.
All Ways Home
A lone pilot searching for home amid starry frescos, And little blood waves that mimic the tide-pull. Our insignificance! Our planet a crumb on the fabric of spacetime,
Sharing the same sky, you and I, wherever feet are anchored. I will write your name on the moon with my fingertips, An apparition cast from memory’s design. Universe-whisper, orange as goldfish. All I want is the delicious scent, the dark blue muddy shoes and ruined grass of starlight, home. Strawberry moon in the cloudless, blue black mystic, one day it could all be rain. Those wind-swept words; voices clutched to our warmth, Courage plucked from conversation.
Breezebreath, feel the blush dust my cheeks, the stars like old photos. Leave the porch light on. The children dance, their mothers sing. Everything changes all at once, the sky, the sun. Bound with images of mystery, like lemongrass and sleep, except for the tree. I look up. I see stars. They live forever inside me. Home is the wild bitterness of backyard blackberries, A bay tree, its fragrant leaves, Breathing easy, A smell so familiar it has none.
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The Gemini North Telescope, one half of the International Gemini Observatory, studies the skies above Maunakea, a mountain in Hawai’i. Its twin, the Gemini South Telescope, is based in the Chilean Andes at Cerro Pachón.
What is it?
According to NOIRLab, both Gemini Telescopes have four imagers and spectrographs that view in both optical and infrared wavelengths simultaneously, which are mounted on the back of the telescopes. These instruments work in sync with the telescopes’ guidance systems in order to be able to look deep into the universe.
The Gemini North Telescope is one of several near the summit of Maunakea and it and its twin are two of only a select few observatories that can be operated fully remotely.
Where is it?
At 13,825 feet (4214 meters) of a long-dormant volcano, the Gemini North Telescope is above clouds and light pollution that could interfere with its analysis.
Satellite streaks form a triangle near the Gemini North Telescope. (Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Pollard)
Why is it amazing?
While the Gemini North Telescope may be at a high enough elevation to avoid light pollution, it has another issue that might interfere with its readings: satellite streaks. Because there are more satellites in low-Earth orbit than before, it can be challenging for astronomers to filter out the activity, from these objects. In this image, the long exposure shows three satellites streaking across the sky to form a triangle shape.
Researchers are working to find ways to track these satellites in hopes of making it easier for astronomers to peer into our universe and study the many celestial objects that are there.
Want to learn more?
You can read more about the Gemini Observatory and satellite activity as astronomers continue to use powerful telescopes to look at our night skies.
Breaking space news, the latest updates on rocket launches, skywatching events and more!
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In a rare celestial alignment, a solar flare erupted just as the International Space Station (ISS) passed in front of the Sun, resulting in a stunning photograph by Arizona-based astrophotographer Andrew McCarthy. Captured from the remote wilderness of the Sonoran Desert, the image is being hailed as one of McCarthy’s finest works to date.
Once-in-a-lifetime moment captured in Sonoran Desert
Known for his detailed composite images of the Sun and Moon, McCarthy set out to photograph a solar transit of the ISS — a fleeting moment when the orbiting space station crosses in front of the Sun from the viewer’s perspective. What he didn’t anticipate was a solar flare erupting in the background at the precise moment of transit.
“While waiting for the ISS to transit the Sun, a sunspot group started flaring, leading to this once-in-a-lifetime shot,” McCarthy wrote on Instagram. He titled the image Kardashev Dreams, a nod to Soviet astronomer Nikolai Kardashev, who introduced the Kardashev scale to measure a civilisation’s technological progress.
“The most detailed solar transit photo I’ve ever done…I call the piece ‘Kardashev Dreams’, representing our first steps to being a much greater civilisation,” he added.
To manage the extreme desert temperatures, which soared to 121°F (roughly 49.4°C), McCarthy said he used ice packs and thermoelectric coolers to prevent his telescopes and computing equipment from overheating. “According to the thermometer in my car it was 121F outside when I got this shot. To mitigate the effects of the heat, I brought ice packs and thermoelectric coolers to help keep the telescopes and computers from overheating.”
The final image, which McCarthy described as a composite mosaic, was created by continuing to photograph the Sun after the ISS had passed. “This is a composite mosaic, as I continued shooting the Sun after the transit to fill in the entire full disc in extreme detail,” he explained. He also revealed that certain elements, including the transition into negative space, were enhanced using material from the 2024 solar eclipse.
“The negative space has some elements composited in from the 2024 eclipse to transition the chromosphere to black, which aides in telling the story of everything happening on the Sun,” McCarthy wrote.
ISS safe from solar flare, despite dramatic imagery
Though visually dramatic, the ISS, which orbits Earth at approximately 400 kilometres, was never in danger from the flare. Experts note that while solar flares can increase radiation levels and affect onboard electronics, they typically pose no immediate threat to astronauts.
The station completes an orbit around Earth roughly every 90 minutes, offering rare opportunities for photographers like McCarthy to capture it crossing the Sun or Moon. These moments last only a fraction of a second, demanding precise timing, high-end gear, and meticulous planning.
Social media erupted with praise for McCarthy’s achievement, with many calling it award-worthy. One user commented, “That’s an absolutely insane shot. Second is favourite,” while another wrote, “This gotta win an award. Where can I vote?”
A third user noted the immense skill and patience behind the image: “The average person will look at this photo and be like that’s awesome but most have no idea how much time effort and planning it took to capture this. Well done sir!”
Responding to a follower who asked how he managed to focus on two objects “billions of kilometres apart,” McCarthy replied, “Millions, not billions. They’re both infinity to the camera. After a few miles everything is, depth of field only applies for close distances while there’s still parallax.”
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Expectations over optical behaviour that have been widely held since Louis Pasteur’s seminal discoveries in 1848 have been upended by a new study. Researchers observed optical behaviours linked to chirality in crystalline lithium cobalt selenium oxide (Li2Co3(SeO3)4), a centrosymmetric crystal that as such cannot be chiral. ‘Within the inorganic crystal community there’s been a strong sentiment that you cannot have chiroptical effects under centrosymmetry,’ says Roel Tempelaar, a researcher at Northwestern University’s chemistry department who led the new work.
Chirality refers to two versions of a structure – be that light, molecules or crystals – that are almost identical but cannot be superimposed on each other, just like your left and right hand. When a structure displays centrosymmetry it has lines of symmetry in every direction from a central point, ruling out any possibility of chirality.
Chiral materials have a chiroptical response – they rotate linearly polarised light and absorb circularly polarised light differently depending on whether it is left-or right-handed – as a result of the molecule or crystal’s shape. Pasteur was able to explain why artificially synthesised tartaric acid did not rotate linearly polarised light, while that derived from biological processes did, as life only produces one version of the molecule. Where both versions are present in equal measure in artificially synthesised tartaric acid, the chiroptical responses cancel out. As centrosymmetric crystals have no chirality in the first place, no-one expected to see chirality in their optical response at all. However, the researchers showed that centrosymmetric crystalline Li2Co3(SeO3)4 transmits more left circularly polarised light than right.
‘This is a really beautiful study that challenges the boundaries of conventional thinking,’ says Richard Robinson, a materials scientist at Cornell University in the US. ‘This result is sure to open exciting new avenues in chiroptic material design.’
How a centrosymmetric crystal shows chiral behaviour
Although, by definition, a centrosymmetric crystal structure does not meet the criteria for a chiroptical response, it turns out that the interference of two other linear polarisation phenomena also results in different absorption of left- and right-handed circularly polarised light. In fact, while the result came as a surprise, reports date back decades when it comes to chiroptical responses based on interference between linear dichroism – polarisation dependent absorption – and linear birefringence – polarisation dependent refraction.
The research community has now come to recognise the effect as a physical mechanism with potentially useful features that differ to the optical activity attributed to chiral molecular or crystal structure. As such it could be exploited for engineering chiral light for quantum information applications, where qubits are encoded in spin states of photons instead of electrons or nuclei. Tempelaar was particularly intrigued by the possibility of exploiting the effect to produce compact chiral lasing. But while there are reports of the effect in organic thin films, metal-halide perovskites and nanostructures, Tempelaar and his team were unable to find any reports of the effect in inorganic crystals, where the prevailing mindset still maintains that chiral crystal structure is a prerequisite for chiroptical responses.
Classy discovery
Being mostly a molecular scientist, Tempelaar was lucky enough to find himself in conversation with a colleague at Northwestern University, Kenneth Poeppelmeier, who has long worked in the realm of inorganic crystals. The two eventually found themselves exploring crystal symmetries theoretically to see in which types of crystal the effect could manifest. ‘To our surprise, we found that it will survive under certain centrosymmetric classes,’ Tempelaar says.
Even so there remained a ‘healthy dose of scepticism’ among the team as they began searching for chiroptical centrosymmetric crystals. A close collaboration between graduate students Katherine Parrish and Andrew Salij, as well as postdoctoral researcher Kendall Kamp, ultimately predicted, synthesised and characterised the candidate crystal Li2Co3(SeO3)4. To their excitement, the measured effect was very large.
‘The magnitude of the effect has significant technological implications,’ says Garth Simpson, who specialises in novel light–matter interactions at Purdue University in the US, but was not involved in this research. He adds that tabulation of crystal classes supporting this effect could be a ‘particularly useful practical guide’ – more so if the table includes all the relevant crystal classes.
Haipeng Lu, whose research at the Hong Kong University of Science and Technology focuses on inorganic functional materials, also notes that the interaction is ‘not new to researchers but has been overlooked for many years’. He says that optoelectronics, photonics, spintronics and quantum information science could all benefit from this discovery. ‘It makes researchers in the field re-think the general idea that only non-centrosymmetric materials can produce circular dichroism.’
Furthermore, Tempelaar is confident the effect is widespread. ‘I don’t think we got particularly lucky – I think this is the tell-tale that there is a whole class of centrosymmetric materials that will be extremely good chiroptical materials,’ he says.
In today’s state of overwhelm, it’s easy to spend more time consumed with the present and the future than contemplating the events of the past. This constant forward motion can, at times, become exhausting and disorienting. We lose our grounding. We miss out on the context and insights that history can provide, and the lessons that may guide us through the tumult of the present. This holds true not just for national history and global history, but also geological history. That is, even events that unfolded millions or billions of years ago can offer insights that remain relevant to our lives and national policies today.
I wrote Strata: Stories from Deep Time to share this geologic lens with readers, and to spotlight the researchers working to untangle some of our planet’s oldest stories. This excerpt explores how scientists first began recognizing that oxygen didn’t billow up into the atmosphere until roughly halfway through Earth‘s existence — and how the arrival of this highly reactive gas fundamentally changed the planet from the seafloor to the stratosphere. By learning how and why oxygen showed up when it did, and how the planet responded to this period of intense global environmental change, we can gain context for the environmental crises unfolding across our planet today — and become better equipped to set ourselves on a more stable path forward.
***
As you read this line, the oxygen you are pulling inside your body makes your body possible. It is allowing you to digest your most recent meal, move your eyes across these words, and think your thoughts. It is the single most important gas to your survival. You share this in common with every other animal on Earth, save for one lone parasite of Chinook salmon that somehow doesn’t need it. Well done, Henneguya salminicola.
Throughout a given day, you fill your lungs with oxygen some 20,000 times. Most of us probably don’t give it much thought. Maybe we assume that this gas has always been here, a given on this highly habitable pale blue dot.
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But it turns out that this dot has not always been highly habitable, nor, for that matter, has it always been blue. The early Earth’s young magma surface sat gooey and cloaked in steam, too hot to hold liquid seas. It took a long time for continents to rise up and for ocean basins to fill in, and far longer still for oxygen to pool up in the atmosphere.
“And so,” writes Rachel Carson in The Sea Around Us, “the rough outlines of the continents and the empty ocean basins were sculptured out of the surface of the earth in darkness, in a Stygian world of heated rock and swirling clouds and gloom.”
Even in those earliest of gloomy days, oxygen — the element O — was all over the place, bound up in molecules like water vapor and quartz and carbon dioxide. It’s the third most abundant element in the universe, and it has been present on Earth since the beginning. But free oxygen — two atoms of O bound together by a pair of shared electrons, liberated from any other material but itself — didn’t emerge as a gas until more than halfway through Earth’s existence.
If you reach out your arms and imagine Earth’s 4.54-billion-year history as a timeline that extends from the tip of your right hand to the tip of your left, the arrival of oxygen gas falls around your heart, at about 2.4 billion years ago, give or take a couple hundred million years.
The fashionably late arrival of oxygen may sound like a planetary sigh of relief. Finally, the possibility for life larger than one cell, with lungs and lips and all the rest of it. But scientists familiar with oxygen’s highly reactive habits suggest its arrival was more like a nightmare.
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As is true of all elements, an atom of oxygen contains a cloud of negatively charged electrons that spin in an arrangement of “shells” around a positively charged nucleus. The outermost electron shell constantly seeks stability by filling to its capacity. In oxygen’s case, its outermost shell is two electrons short — comparatively fewer than other elements — and the configuration of those electrons contribute to oxygen’s high reactivity. Oxygen’s electron cloud is also relatively thin compared to other elements. Without much of a barrier between it and the outside world, the positive pull of the nucleus easily seeps out and lures in the negative charges of the two electrons it needs to stabilize. Two atoms of oxygen bound together as oxygen gas have a pull similarly as strong as a single atom on its own.
When oxygen first appeared on Earth, it desperately rooted out and bonded with anything willing to share its electrons, fundamentally changing the materials it bonded with. It weaseled into microbial cells and mutilated their machinery. It sulked into currents and eddies and made arsenic more soluble, it spread hydrogen peroxide poisons into DNA. With all the havoc it wreaked, this gas might have initiated one of the worst mass extinctions in all of Earth history — though it’s hard to know this for sure, since the single-celled beings that would have gone extinct were too squishy to leave behind reliable fossils. Even so, some call this geologic moment the Oxygen Catastrophe.
Over time, molecules from the bottom of the ocean to the top of the atmosphere grew to accept oxygen’s reactivity, and living things evolved ways to cope with this new gas. Their cells grew to tolerate it, and then to depend on it. They used it to break down food and generate energy that allowed them to grow larger and more complex, with multiple cells that communicated across newly sophisticated membranes. These oxygen-fueled innovations expanded and cascaded and eventually led to the evolution of eyeballs and brains and lungs and lips and, over billions of years, the possibility of us.
So what, exactly, happened around 2.4 billion years ago? Why did oxygen arrive when it did? And how can we read this in the rock record?
Courtesty of W. W. Norton & Company
THE SEARCH FOR OXYGEN’S origin began with a problem. When Charles Darwin published On the Origin of Species in 1859, he agonized over the seeming absence of fossils in the planet’s oldest rocks. The ages of rocks at this time were known only in a relative sense — as in, what formed first and what followed. The scientific law of superposition, proposed by Danish geologist Nicolas Steno in the seventeenth century, helped clarify that younger strata always sit atop older strata, since that’s how sediments accumulate in lake beds and seafloors and so on.
As hard as paleontologists of that time looked, they couldn’t find any remnants of ancient life in the oldest, bottom-most strata that they examined. Then bits and bobs appeared in what looked like an explosion of living things in strata above a certain age. This troubled Darwin deeply. Any such explosion of life undermined his theory of natural selection, a process of elimination that he argued should inherently take a very long time to unfold. By his estimations, it could never have taken place as instantaneously as those earliest fossils suggested.
Halfway through On the Origin of Species, he gravely acknowledged the implications of this predicament. “The case at present must remain inexplicable[,]” he wrote, “and may be truly urged as a valid argument against the views here entertained.”
But here we are, still entertaining Darwin’s views more than 150 years later. And that is thanks largely to rocks discovered not long after World War II.
At the end of the war, a wave of mineral exploration arose across the world to meet the needs of rapidly expanding economies. Federal agencies hired geologists to scour continents for oil, gas, and coal to fuel those economies, along with metals like iron and uranium to build up arsenals of defense. This was of national interest, not just private economic interest.
As geologists marched around the globe and sketched up their maps of these resources, they noticed other curious details about the planet’s history. That is, in their search for the materials that humans desired, they found inklings of how we got to be here desiring anything in the first place.
In the summer of 1953, Wisconsin geologist Stanley Tyler was studying iron-rich rocks on the north shore of Lake Superior in Canada when he took a Sunday off to rent a boat and go fishing. While his lure bobbed in the water, he absently noted the shapes and colors along the shore, as any geologist might. One outcrop caught his eye, so he motored over to take a closer look.
Tyler recognized the deposit as an extension of the Gunflint Chert, a rock formation with the texture of tightly packed brown sugar and the contents of ancient seafloor sediments. Cherts can take on a whole range of colors depending on the conditions they form within, from beige to red to green to other hues in between. Most of the chert that Tyler had found on that trip had been maroon, but this outcrop caught his eye for its striking shade of jet black. He knew that the color black in rocks was sometimes indicative of organic material, remnants of ancient life.
He lopped off a chunk, stashed it in his boat, and motored on.
Back at his lab in Madison he placed a sliver of that black chert under a microscope, and found shapes that did not speak the language of minerals. The rods, spheres, and squiggles he found did, as he suspected, look more lifelike than lithic.
Based on geologic maps of the region, he knew these rocks had formed during the allegedly fossil-free epoch that had so troubled Darwin. Tyler’s gut told him he may have just found some of the earliest evidence of life ever discovered, but he was a mineralogist more than a paleontologist and so he needed a second opinion.
That fall, he took photographs of his findings to a geology conference in Boston and shared them with a couple of colleagues. One among them, a Harvard paleobotanist named Elso Barghoorn, agreed that the samples looked rather lifelike, and the two published a short paper describing what they had found.
This publication quadrupled the length of the fossil record. It was groundbreaking, but was brief and preliminary. They needed more time to study the fossils to do justice to the scope of their findings.
For years, they didn’t make progress on a follow-up paper. A decade went by and, in 1963, Tyler passed away at the age of 57 from heart complications, without the satisfaction of sharing his discoveries more completely with the world. By 1965, an impatient colleague named Preston Cloud — a bantamweight boxing champion turned acclaimed Earth historian — threatened to beat Barghoorn to the punch with his own paper on the fossils. That was enough to push Barghoorn into gear. He rushed to complete a manuscript and published it in the journal Science a couple months before Cloud published his.
“For all of time it will probably stand as the most important article ever written in the field . . . ,” writes William Schopf, a graduate student who helped Barghoorn pen that manuscript, but who humbly declined authorship himself because he didn’t feel he had contributed enough.
Spurred by this new paper on the Gunflint Chert, geologists went searching for evidence of ancient life in black cherts around the world. Papers flooded out, claiming to have solved Darwin’s dilemma and showing how fossils had been in those seemingly lifeless rocks all along — they had simply been microscopic. The theory of natural selection persevered, and the lengthy record of our ancient roots began to fill out.
But while those microscopic rods and squiggles resolved one nagging dilemma, they opened up a slew of other questions. What, exactly, were those fossils? What kind of world did they evolve into? And what kind of world did they create with their growth?
Around the same time that these questions began bubbling up, another set of observations from the rock record thickened the plot of the squiggles. Geologists were compiling evidence that, before those lifeforms lived, the planet’s atmosphere had no oxygen gas in it at all. Minerals that disintegrate in the presence of oxygen were found locked up in ancient riverbeds older than a certain age. Then, around the time they believed those squiggles showed up on the scene, those riverbed minerals disappeared and the very first, rusty red fingerprints of oxygen began appearing in strata around the world.
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Perhaps, some reasoned, those squiggles were responsible for painting the world’s soil and seafloor sediments red, by ushering in the very first poofs of oxygen. And perhaps, in their delivery of this gas, they catapulted Earth out of its original barrenness and into the tangle of complex life we know today.
