More than 350 million years ago, Earth was ruled by fish, some up to 10 metres long.
But a mass extinction stretching across millions of years killed up to 80 per cent of all species that existed at that time, bringing an end to the Devonian Period.
Scientists have come up with numerous theories over the years for why this extinction might have occurred, such as volcanic activity, meteorites or rapid global warming.
Now, new research is bringing a new possibility to the forefront: what if a supernova was responsible?
A paper published Tuesday in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) details the brand new theory, and how it could feasibly be proven — or ruled out.
The Devonian Period occurred from roughly 416 million to 358 million years ago. The world looked vastly different then, characterized by two supercontinents, Gondwana and Laurussia, which would eventually combine to form Pangaea.
Part of the Paleozoic Era, the Devonian Period is also called The Age of Fishes, as biodiversity exploded within Earth’s oceans during this time. The ancestors of sharks had their beginning in the Devonian, and a fossilized creature from the Devonian period found in the Canadian Arctic in 2004, called a tiktaalik, is thought to be a “vital link between fish and the first vertebrates to walk on land,” according to National Geographic.
During the Late Devonian period, there was a huge loss of biodiversity that occurred over millions of years. Two extinction pulses, the Kellwasser event and, around 10 million years later, the Hangenberg event, are thought to have finished off the Devonian period for good, leading the planet into the Carboniferous Period.
The Hangenberg Crisis refers to a confluence of events that had a catastrophic effect on the living things of that time. There was a widespread issue with the oceans losing a high percentage of oxygen, called an ocean anoxic event, creating massive dead zones within the seas. There was also a dramatic fall in the sea level around the same time.
According to Tuesday’s paper, recent evidence has suggested that the Hangenberg event at the end of the Devonian was also associated with a depletion of the stratospheric ozone — the layer that filters out dangerous ultraviolet radiation from the Sun.
The new research theorizes that a supernova millions of miles away could have bombarded the planet with ionizing radiation, causing the depletion of the ozone.
A supernova is when a dying star of massive proportions explodes, creating either a neutron star or a black hole in its place, and firing a shock wave of elements, gas and charged particles out into the galaxy.
The researchers believe that if a supernova is responsible, it would have been within around 20 parsecs, or 66 lightyears, of Earth, “somewhat beyond the “kill distance” that would have precipitated a full mass extinction.”
Numerous massive stars capable of producing supernovas live in the Milky Way. A supernova within the distance that researchers have posited would have sent cosmic rays washing over the Earth for around 100,000 years.
“The cosmic ray intensity would be high enough to deplete the ozone layer and induce UV-B damage for thousands of years,” the researchers wrote.
They pointed out that while ozone depletion caused by enhanced convection — one of the other theories surrounding the extinction — is generally geographically limited and episodic, ozone depletion caused by a supernova would be “long lived and global and is therefore much more likely to lead to an extinction event.”
Although ionizing radiation from space is known to be a possible cause of ozone depletion, the research says, this theory has never been applied to this particular mass extinction before.
But is there a way to prove this theory? Researchers say there is, if we inspect the distinct layer of rock in the Earth’s crust that corresponds to the Devonian Period, where fossils and preserved material can allow us to peer into the extinction itself.
If a supernova caused by the core collapse of a massive star was close enough to cause this mass extinction, it would also have peppered supernova “debris” over the Earth as “micron or submicron-sized particles created early after the explosion.”
This would’ve left radioactive isotopes on Earth — distinct versions of chemical elements that are unstable and emit radiation as they decay.
Different radioactive isotopes have different lifespans, meaning “those with lifetimes comparable to the time since the event would provide suitable signatures,” if found within fossils or rock from the Devonian Period.
Researchers speculate that two of the long-lived radioisotopes that could’ve been deposited on Earth — and would be still detectable today — could be samarium-146, and plutonium-244.
The end of the Devonian Period, spurred on by numerous extinction events that severely cut down the level of biodiversity in Earth’s oceans, is still a mystery right now. But if scientists can find these radioisotopes, it may mean that supernovas have played a greater role in our planet’s history and evolution than we ever knew.
How to watch historic SpaceX rocket launch more Starlink satellites Friday – CNET
The Falcon 9 rocket booster that sentin May is scheduled to get recycled again Friday, when SpaceX plans to send 60 more to orbit atop its column of fire.
Elon Musk’s trademark reusable rocket will be making its third flight when it lifts off from Florida’s Kennedy Space Center at 10:57 a.m. PT (1:57 p.m. ET). This specific unit sent astronauts Doug Hurley and Bob Behnken to orbit in May and thenin July. So far, SpaceX has managed to launch and land the same rocket up to .
The launch was originally scheduled for Thursday, but it got scrubbed and pushed back a day due to a “recovery issue.” It could be that SpaceX didn’t like the look of the weather in the Atlantic where the first stage and the fairing were set to be recovered.
One half of the nose cone, or fairing, atop the rocket has also seen two previous flights, both of them earlier Starlink missions.
This should be a fairly routine launch. It will be the 13th Starlink mission so far, and SpaceX is ultimately planning on dozens more as it grows its broadband mega-constellation.
Following the launch and separation of the rocket’s second stage and payload, the first-stage booster will again return to Earth to land on a droneship in the Atlantic.
SpaceX will stream the entire thing via the feed above, starting at about 10 minutes before launch.
Scientists Find Efficient Way to Convert Carbon Dioxide into Ethylene | Chemistry, Materials Science – Sci-News.com
A team of U.S. researchers has developed copper nanowires with rich surface steps to catalyze a chemical reaction that reduces carbon dioxide (CO2) emissions while generating ethylene (C2H4), an important chemical used to produce plastics, solvents, cosmetics and other important products globally.
“The idea of using copper to catalyze this reaction has been around for a long time, but the key is to accelerate the rate so it is fast enough for industrial production,” said co-lead author Professor William Goddard III, a researcher in the Department of Applied Physics and Materials Science at Caltech.
“This study shows a solid path towards that mark, with the potential to transform ethylene production into a greener industry using carbon dioxide that would otherwise end up in the atmosphere.”
Using copper to kick start the carbon dioxide reduction into ethylene reaction has suffered two strikes against it.
First, the initial chemical reaction also produced hydrogen and methane — both undesirable in industrial production.
Second, previous attempts that resulted in ethylene production did not last long, with conversion efficiency tailing off as the system continued to run.
To overcome these two hurdles, Professor Goddard III and colleagues focused on the design of the copper nanowires with highly active steps — similar to a set of stairs arranged at atomic scale.
One intriguing finding of this collaborative study is that this step pattern across the nanowires’ surfaces remained stable under the reaction conditions, contrary to general belief that these high energy features would smooth out.
This is the key to both the system’s durability and selectivity in producing ethylene, instead of other end products.
The scientists demonstrated a carbon dioxide-to-ethylene conversion rate of greater than 70%, much more efficient than previous designs, which yielded at least 10% less under the same conditions.
The new system ran for 200 hours, with little change in conversion efficiency, a major advance for copper-based catalysts.
In addition, the comprehensive understanding of the structure-function relation illustrated a new perspective to design highly active and durable carbon dioxide reduction catalyst in action.
“We are at the brink of fossil fuel exhaustion, coupled with global climate change challenges,” said co-lead author Professor Yu Huang, a researcher in the Department of Materials Science and Engineering at the University of California, Los Angeles.
“Developing materials that can efficiently turn greenhouse gases into value-added fuels and chemical feedstocks is a critical step to mitigate global warming while turning away from extracting increasingly limited fossil fuels.”
“This integrated experiment and theoretical analysis presents a sustainable path towards carbon dioxide upcycling and utilization.”
The team’s paper was published in the journal Nature Catalysis.
C. Choi et al. Highly active and stable stepped Cu surface for enhanced electrochemical CO2 reduction to C2H4. Nat Catal, published online September 7, 2020; doi: 10.1038/s41929-020-00504-x
NASA mulls Venus mission after recent discoveries | Reuters Video – Reuters UK
NASA is considering approving by next April up to two planetary science missions from four proposals under review, including one to Venus that scientists involved in the project said could help determine whether or not that planet harbors life. Freddie Joyner has more.
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