New Scientist - USA (2019-10-12)

54 | New Scientist | 12 October 2019

End of an era

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?

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

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. ❚

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

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

The back pages Almost the last word

LE

SL

EY

M

AG

NO

/G

ET

TY

IM

AG

ES

Why do unfamiliar faces

feature in some dreams?