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planet,” he explains.
The prevailing model to explain this mountainous
ring is that following the initial impact there was some
kind of rebound of fractured rocks at the centre of
the crater, which rippled outwards before eventually
coming to a stop. To picture this, think of what
happens when you throw a stone into a pond.
Superficially, the rock in these deeper cores looks

just like normal granite, says Morgan. “Except when

you look closely, it’s very highly fractured,” she says.

“It has a very strange set of physical properties.

I think it’s going to explain to us how rocks that are

really hard are weakened enough to be able to move

many, many kilometres during this impact event.”

The cores, and all the valuable clues they contain,

are on their way to Bremen in Germany, where the

scientists will regroup in September to break them

open and begin the analysis proper. It seems likely

that each will be dealt with in sequence, from core 1

all the way through to core 303.

For scientists like Chris Lowery, who are eagerly

waiting to delve into core 40 at the top of the impact

layer, “cores 1 through 39 are going to be an exercise

in patience”. But if core 40 lives up to its promises, the

wait will surely be worth it. ß

ABOVE: Dust from

the impact cloaked

the entire planet in

darkness, leading

to the widespread

collapse of food

webs

In 1980, Nobel Prize-winning

physicist Luis Alvarez and his

team discovered a thin layer

of iridium blanketing Earth at

precisely the moment when the

dinosaurs disappeared from the

fossil record. As iridium is one

of the rarest elements in Earth’s

crust, but is found in asteroids

in far higher concentrations,

the scientists imagined vast

quantities of dust (including

extraterrestrial iridium) propelled

high into the stratosphere and

distributed worldwide.

“The resulting darkness would

suppress photosynthesis,” they

wrote in Science, which would

have led to the rapid collapse

of food webs and the demise of

the dinosaurs. A decade later,

in 1990, geologists identified

Chicxulub in the Gulf of Mexico as

the most likely site of this impact.

Few scientists now dispute

the terminal consequences

of the Chicxulub event for

many species, but there is also

evidence to suggest that other

factors could have been part

of the dinosaurs’ demise. The

Deccan Traps, in what is now

central India, are one of the

largest volcanic features on

Earth. There is some uncertainty

over exactly when they formed

• it could have been just before
  the asteroid impact or as a
  result of the aftershock – but
  the volcanic gases released
  would have had a chilling effect
  on the climate. It seems likely
  that the Chicxulub impact
  would also have triggered a
  wave of secondary events, like
  earthquakes, megatsunamis,
  wildfires, volcanism and acid
  rain, that could all have helped
  push Earth’s reptilian rulers
  over the edge.

WHAT REALLY KILLED

THE DINOSAURS?

HENRY NICHOLLS IS A SCIENCE WRITER AND AUTHOR. HE TWEETS FROM

@WAYOFTHEPANDA