An Open University research student will reveal her findings on what caused one
of the world’s ‘Big Five’ mass extinctions at the Geological Society of
America’s annual meeting in Denver, USA, this month.
PhD student Charlotte Pearce will input into the debate as to whether a
meteorite impact or volcanic eruption caused the Cretaceous Tertiary Boundary
(KTB) mass extinction 65-million-years-ago.
Between 50 and 60 per cent of marine and terrestrial life-forms became extinct
during the KTB extinction, including the dinosaurs.
The cause of this mass extinction has received much attention from scientists
over the last 25 years, since the detection of iridium-rich cosmic debris at the
boundary layer around the world — an element known to be rare on earth. This
led to the theory that a meteorite impact could have been responsible for the
debris and the mass extinction; the 180 km wide Chicxulub impact crater was
eventually discovered in the Gulf of Mexico.
However, on the other side of the world, massive volcanic eruptions, known as
the Deccan Traps continental flood basalt province, were simultaneously reaching
their peak, forming a 2.5km thick pile of lava.
“Both the Chicxulub impact and the Deccan eruptions would have had the potential
to induce detrimental environmental changes serious enough to significantly
affect terrestrial ecosystems,” says Charlotte.
“Dust-induced darkness, acid rain, wild fires and global warming would all have
played a role in inducing biospheric trauma, but the timescales over which these
were effective would be expected to be different, dependent on the event that
caused them,” she adds.
Charlotte used chemical and isotopic fingerprinting techniques on molecular
fossils from North America, and more recently from New Zealand, to investigate
patterns which would establish whether there was instantaneous change (as the
result of a meteorite impact) or gradual change within the ecosystem (as caused
by prolonged volcanism).
“Carbon isotopes can tell us a lot about the stability of an ecosystem and,
together with the identification of molecular fossils, enables past variations
in habitat, climate and biology to be investigated.
“The aim of my project is to compare and contrast samples from several
terrestrial and marine KTB successions, at varying palaeogeographical distances
from the locations associated with the two putative causes of end-Cretaceous
environmental stress. In effect the project examines the effects of these two
environmental disasters working outwards from the ‘ground zero’ locations,” says
Charlotte.
Results taken from samples in the Western Interior of North America show that
the ecosystem experienced a short sharp shock at the boundary consistent with a
meteorite impact. Early analysis of the New Zealand samples also point to a
meteorite impact.
