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The back pages Almost the last word Why do unfamiliar faces feature in some dreams?
End of an era
Mike Follows Sutton Coldfield, West Midlands, UK The theropod dinosaurs evolved into birds and survive to this day. But the Chicxulub asteroid that rammed into Earth just off the Yucatán peninsula in Mexico 66 million years ago led to the extinction of 75 per cent of all species living at the time. It isn’t possible to be certain of conditions after the impact but it seems likely that it would have created a massive plume of vaporised rock. Within hours, this probably condensed into a rain of molten rock. This in turn could have killed most organisms out in the open and ignited global wildfires. That means animals in caves, underground or in water stood a better chance of surviving the first few hours. For many, surviving simply prolonged their demise because the dust that was lofted into the stratosphere blocked out sunlight, cooling the globe and reducing photosynthesis, leading to the collapse of food chains. Once the dust settled, Earth would have experienced global warming because of the release of carbon dioxide into the atmosphere from the wildfires. It is possible that most of the extinctions may have happened within months of the impact. J. David Archibald Professor emeritus of biology, San Diego State University, California The more than 10,000 species of living birds are descendants of the survivors of the asteroid impact. But dinosaurs were already in decline. In the 10 million years before the impact, the number of species almost halved. A likely cause is the loss of habitats due to the retreat of inland seas and climate change caused by 54 | New Scientist | 12 October 2019
LESLEY MAGNO/GETTY IMAGES
Dinosaurs went extinct 66 million years ago, apparently as a result of an asteroid impact. How much time elapsed between that event and the death of the very last dinosaur?
This week’s new questions Dreamy looks Strangers appear in my dreams. Their features are clear, but none are familiar, not even from an earlier dream. What is going on in my brain, and do others experience the same? Andrew Ferrier, Eardiston, Worcestershire, UK New for old The roll-out of low-emission zones in the UK encourages us to replace cars with newer, lower-emission models. Taking manufacturing into account, how long would it be before reduced emissions make a new car less polluting than keeping the old one? Karen Pearson, Edinburgh, UK
volcanism in the Deccan Traps on the Indian subcontinent. Remaining species of dinosaurs appear to have been doing fine until the Chicxulub asteroid struck. For scale, the Pinatubo eruption in 2001, which injected large amounts of ash and gas high into the atmosphere that spread worldwide, caused an average global cooling of 0.6 °C. The asteroid impact had a cooling effect many magnitudes greater. Brian King Barton on Sea, Hampshire, UK As the author Mark Twain once said, reports of my death are greatly exaggerated. Dinosaurs are alive and well in a chicken coop near you. Seth Paddle Melbourne, Australia In New Zealand, a region that was far from Chicxulub at the time of the impact, a full ecological suite of dinosaurs survived for another million years. Jeffrey Stilwell at
Monash University in Australia and colleagues have found three herbivorous and two carnivorous species. It is interesting to reflect on what prevented the resurgence of dinosaurs from this base.
Fresh fruit Most fruit and vegetables sold in supermarkets come with a label saying “wash before eating”. What are the risks of eating unwashed produce and does a quick sluice under the tap reduce them significantly?
Simon Goodman Griesheim, Germany Fruit and vegetables can have contaminants from three sources on their surface: soil, human handling and their own
microbiome. All are a potential source of pathogens for us, but those with a compromised immune system, such as older people and pregnant women, are most likely to be affected. It is possible that some microbes on fruit and veg are helpful, especially those of the plant’s microbiome, which may help boost our immune system. A minority of bacteria and fungi in soil are potentially harmful, including those causing botulism, tetanus, listeriosis and histoplasmosis. Meanwhile, the vegetable microbiome is complex, and in one German study 4 per cent of sampled lettuces were found to be colonised by E. coli. Washing lettuce, including using detergents or disinfectants, was reported not to help remove such contamination – but might get rid of soil and bacteria left by people during handling. Chris Daniel Glan Conwy, Conwy, UK The UK National Health Service advice is to rinse fruit and veg in running water for 30 seconds and rub the surface gently in a bowl of water, using a soft brush if needed to remove any soil. This is claimed to remove most bacteria and pesticides. More effective methods are to soak produce in a 10 per cent salt water solution, vinegar or a 1 per cent solution of sodium bicarbonate, then rinse. Washing your hands before and after preparing fruit and veg and cleaning chopping boards are also advised. And it is recommended that fruit is washed only as it is used, not as soon as it is brought home, because increased moisture can itself be a breeding ground for bacteria and mould. ❚
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms
End of an era
Mike Follows Sutton Coldfield, West Midlands, UK The theropod dinosaurs evolved into birds and survive to this day. But the Chicxulub asteroid that rammed into Earth just off the Yucatán peninsula in Mexico 66 million years ago led to the extinction of 75 per cent of all species living at the time. It isn’t possible to be certain of conditions after the impact but it seems likely that it would have created a massive plume of vaporised rock. Within hours, this probably condensed into a rain of molten rock. This in turn could have killed most organisms out in the open and ignited global wildfires. That means animals in caves, underground or in water stood a better chance of surviving the first few hours. For many, surviving simply prolonged their demise because the dust that was lofted into the stratosphere blocked out sunlight, cooling the globe and reducing photosynthesis, leading to the collapse of food chains. Once the dust settled, Earth would have experienced global warming because of the release of carbon dioxide into the atmosphere from the wildfires. It is possible that most of the extinctions may have happened within months of the impact. J. David Archibald Professor emeritus of biology, San Diego State University, California The more than 10,000 species of living birds are descendants of the survivors of the asteroid impact. But dinosaurs were already in decline. In the 10 million years before the impact, the number of species almost halved. A likely cause is the loss of habitats due to the retreat of inland seas and climate change caused by 54 | New Scientist | 12 October 2019
LESLEY MAGNO/GETTY IMAGES
Dinosaurs went extinct 66 million years ago, apparently as a result of an asteroid impact. How much time elapsed between that event and the death of the very last dinosaur?
This week’s new questions Dreamy looks Strangers appear in my dreams. Their features are clear, but none are familiar, not even from an earlier dream. What is going on in my brain, and do others experience the same? Andrew Ferrier, Eardiston, Worcestershire, UK New for old The roll-out of low-emission zones in the UK encourages us to replace cars with newer, lower-emission models. Taking manufacturing into account, how long would it be before reduced emissions make a new car less polluting than keeping the old one? Karen Pearson, Edinburgh, UK
volcanism in the Deccan Traps on the Indian subcontinent. Remaining species of dinosaurs appear to have been doing fine until the Chicxulub asteroid struck. For scale, the Pinatubo eruption in 2001, which injected large amounts of ash and gas high into the atmosphere that spread worldwide, caused an average global cooling of 0.6 °C. The asteroid impact had a cooling effect many magnitudes greater. Brian King Barton on Sea, Hampshire, UK As the author Mark Twain once said, reports of my death are greatly exaggerated. Dinosaurs are alive and well in a chicken coop near you. Seth Paddle Melbourne, Australia In New Zealand, a region that was far from Chicxulub at the time of the impact, a full ecological suite of dinosaurs survived for another million years. Jeffrey Stilwell at
Monash University in Australia and colleagues have found three herbivorous and two carnivorous species. It is interesting to reflect on what prevented the resurgence of dinosaurs from this base.
Fresh fruit Most fruit and vegetables sold in supermarkets come with a label saying “wash before eating”. What are the risks of eating unwashed produce and does a quick sluice under the tap reduce them significantly?
Simon Goodman Griesheim, Germany Fruit and vegetables can have contaminants from three sources on their surface: soil, human handling and their own
microbiome. All are a potential source of pathogens for us, but those with a compromised immune system, such as older people and pregnant women, are most likely to be affected. It is possible that some microbes on fruit and veg are helpful, especially those of the plant’s microbiome, which may help boost our immune system. A minority of bacteria and fungi in soil are potentially harmful, including those causing botulism, tetanus, listeriosis and histoplasmosis. Meanwhile, the vegetable microbiome is complex, and in one German study 4 per cent of sampled lettuces were found to be colonised by E. coli. Washing lettuce, including using detergents or disinfectants, was reported not to help remove such contamination – but might get rid of soil and bacteria left by people during handling. Chris Daniel Glan Conwy, Conwy, UK The UK National Health Service advice is to rinse fruit and veg in running water for 30 seconds and rub the surface gently in a bowl of water, using a soft brush if needed to remove any soil. This is claimed to remove most bacteria and pesticides. More effective methods are to soak produce in a 10 per cent salt water solution, vinegar or a 1 per cent solution of sodium bicarbonate, then rinse. Washing your hands before and after preparing fruit and veg and cleaning chopping boards are also advised. And it is recommended that fruit is washed only as it is used, not as soon as it is brought home, because increased moisture can itself be a breeding ground for bacteria and mould. ❚
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms