14
Science and technology
A
team of European scientists have worked out the
time of year when a huge asteroid struck Earth
66 million years ago, and say it could help explain
why the impact destroyed so many living things. The
asteroid, which hit Mexico’s Yucatán Peninsula, was
the final blow in the extinction of the dinosaurs that
had ruled Earth for 170 million years. It left birds as
the only surviving dinosaur relatives and cleared the
way for the expansion of mammals (warm-blooded,
usually furry animals that make milk for their young).
Until now, experts have struggled to explain just
why some species survived and others didn’t.
The new research offers important clues.
It suggests the asteroid struck in
spring for the northern half of
the world – a time when many
animals were emerging from
the snug winter burrows
that might otherwise have
protected them.
The evidence that places
the asteroid impact in spring
comes from a remarkable site
called Tanis, in the US state of
North Dakota. Here, scientists
have found the fossils (preserved
remains turned into rocky minerals)from fish that died as their gills were choked with
debris falling from the impact itself. A team led by
Marianne During of Uppsala University in Sweden
realised that the fish grew their bones more at some
times of year than others. By looking at the state of
the fossilised bones, the team could work out the
season when the fish had died.
The impact caused an enormous blast of heat
and fires that probably killed most large animals
immediately. Small animals living closer to the impact
site, and those that were waking up in spring, would
also have died almost instantly. Then, as dust from the
explosion spread through the air and blocked
out the Sun’s heat and light, the whole
planet was plunged into a long
period of cold and darkness.
This killed plants and led both
plant-eating and meat-eating
animals to die off – about
76% of all species. If smaller,
southern-hemisphere
animals were already in their
winter shelters when the
asteroid struck, those that could
find food when they emerged
months later might have spread
across the recovering planet.Dino killer struck in spring
First discovered in 2008, the Tanis fossil site
in North Dakota is named after an ancient
Egyptian city that is the burial place of a deadly
treasure in the famous film Raiders of the Lost
Ark. Signs of a prehistoric river have been found
preserved in the rocks at the site. The area was
shaken by huge earthquakes when the asteroid
struck about 1,900 miles further south. It was
then covered in fragments of molten rock,
which sprayed out from the impact and cooled
into tiny, glassy droplets. Fossils found at the
site since 2012 include the jumbled remains of
several dinosaurs, flying and marine reptiles,
fish, insects and plants.Tanis: frozen in time
An artist’s impression
of just before the smash.Impact debris now forms a
distinct layer in Earth’s rocks.Fish fossils
from Tanis.DEEP
IMPACT
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eep.The Week Junior • 5 March 2022