It is believed that there have been at
least fi ve mass extinctions in the last
540 million years, the most famousbeing the one that signalled the end of the
Cretaceous period around 65.5 million years ago
and effectively w iped out the dinosaurs.
Palaeontologists initially believed that thismass extinction event was caused by climate
and geological changes. This theory changed in
the 1980s when scientists Luis and Walter
A lvarez discovered a layer of iridium in the
geological record that corresponds with the
time that the dinosaurs became extinct. This
substance existed only in space and so its
presence on Earth must have come as a result of
a comet, asteroid or meteor colliding with
Earth. The discover y of the colossal Chicxulub
Crater in Mexico’s Yucatán Peninsula that dates
back to the time of the mass extinction adds
signifi cant weight to this theory.
As a result, the Earth suffered a series of
volcanic eruptions. Research has shown that
the common factors in mass extinctions include
large-scale lava fl ow and volcanic gases, which
desecrate the land and suck all of the ox ygen
out of our oceans. The gases coughed out of
volcanic eruptions, most notably carbon
dioxide, are linked to short-term regional
warming, acid rain and ozone depletion – the
perfect cocktail to snuff out any creature.Based on the fossil record, mass extinctions
are followed by recover y. Follow ing the events
of the Cretaceous period that rendered the
dinosaurs extinct, the gradual recover y of
vegetation was ev ident by the discover y of fern
spores. Plants managed to adapt to cope with
conditions on Earth. The fossil record tells us
that the last dinosaur to walk the Earth was the
Cor y thosaurus. This herbivore stood upright,
with two arms used to strip and devour
vegetation and was easily identifi able by a
decorative semicircular crest on its head. Much
effort has been spent searching for the causes of
mass extinctions because ultimately there is no
reason why another couldn’t occur again.DINOSAURS’ LEGACY
The death of the dinosaurs
The death of the dinosaurs
Loads of theories surround the death of the dinosaurs, we get to the bottom of it
Atmosphere
The volcanic
eruptions added
more carbon
dioxide to the air,
sucking the oxygen
out of the water