PLANET EARTH GLOBAL EYE | Supernova sparked mass extinction 359 million years ago | Stone forests formation

 supernova sparked mass extinction 359 million years ago

    A global extinction event that occurred around 359 million years ago may have been triggered by the death blast of a distant star. Towards the end of the Devonian Period, 416 million to 358 million years ago, there was a mass extinction known as the Hilgenberg event; it wiped out armored fish called placoderms and killed off approximately 70 per cent of Earth’s invertebrate species. But scientists have long puzzled over what caused the event.

    Recently preserved plant spores offered clues about this ancient extinction. Fossil spores spanning thousands of years at the boundary of the Devonian and the Carboniferous periods showed signs of damage caused by ultraviolet (UV) light. This find suggested that a cataclysmic event had caused a long-lasting disruption of Earth’s ozone layer, which shields the planet from harmful UV rays. Scientists proposed that a likely candidate for this blast of UV light could be one or more supernovae that exploded within 65 light years of Earth.

    Climate change and extreme volcanic activity can also damage the ozone layer, but evidence in the geologic record at the end of the Devonian Period couldn’t clearly link the ozone depletion to a global disaster that originated on Earth. 

    When stars die they release blasts of UV light, X-rays and gamma rays. If a supernova is close enough to Earth, these rays can shred the ozone layer, exposing Earth to unfiltered UV light from the Sun and harming life on the planet’s surface. However, this damage is typically short-lived. Its effects fade after a year or so, “and after a decade, Earth restores its ozone,” said Brian Fields, a professor in the department of astronomy at the University of Illinois at Urbana-Champaign

    But that initial bombardment is just the first stage of the damage a neighboring supernova can inflict. “Later the supernova blast slams into the Solar System. The blast acts as a particle accelerator, and Earth is bathed with an intense rain of high-energy particles,” which are known as muons, Fields said. Not only does this blast strip away Earth’s ozone layer again, muons then irradiate Earth’s surface and penetrate deep underground and into the oceans. “These will damage life, and the cosmic rays will linger for many thousands of years – up to 100,000 years,” Fields said. If a nearby supernova – or more than one – shredded Earth’s ozone layer, that could explain the UV damage found in Late Devonian spores and pollen over millennia.

    “Work by my co-authors and others has shown that a supernova about 25 light years away would lead to biological cataclysm… a true mass extinction,” Fields said. “For context, the nearest star today is four light years away,” he added. As the Hangenberg extinction was less severe than other mass extinctions in Earth’s history, it’s estimated that the Devonian supernova would have exploded about 65 light years away. 

    However, there is not yet a potential candidate for a star in this range that died 359 million years ago. The good news is that you don’t need to worry about a supernova upending life as we know it – at least not anytime soon.

Stone forests formation shown with rock candy

    The stunning, razor-sharp spires of stone forests can forming deceptively simple conditions, a sugary new experiment has found. Using sticks of candy, researchers discovered that cylindrical shapes can naturally sharpen into points in Stillwater as they dissolve, with no complicated flow required. This phenomenon could explain why sharp stone pinnacles are often found where easily dissolvable limestone rock predominates. 

    “We found the simplest recipe for how to make one of these pinnacles,” said Leif Restripe, an experimental physicist and mathematician at New York University.  

    The recipe was simple indeed. Restripe and his team cooked up hard candy, like a lollipop, in the shape of a cylinder with a domed top. They stuck the candy upright in a tank of water and simply let it dissolve. You might imagine that the candy would simply shrink away, staying more or less the same shape. But that’s not what happened. Instead it gradually sharpened into a point as it dissolved, and these points could become quite sharp.

    The next step was to do the math to figure out why this sharpening effect occurred. As the candy dissolves, the water directly next to the sugar column becomes laden with sugar. This makes it heavier than the surrounding water. This sugar-laden water sinks downwards, almost like a skin sloughing off the candy.

    This sinking means that the dissolving candy essentially creates its own flow. Fresh water flows in from the sides, only to become laden with sugar itself and sink. The flow is what sharpens the candy into a point.

    Limestone and other dissolvable rock are more complex than simple sugar, though, and there are likely other factors that help shape the stone forests found around the world. Rock chemistry, loose sediment and winds likely play a role. But the stone forests largely form while submerged under water, and the simplicity of the candy experiment helps explain the basic process. “Our choice of materials here, as pure water and pure candy, it is purposefully clean so we can understand it in terms of the fundamentals,” Restripe said.