Burren and Cliffs of Moher UNESCO Global Geopark - Geology

Shell ornament on one of the extinct fossil ammonoids found in the rocks of west Clare.
Mass Extinctions
The spectacular end of most dinosaurs around
65 million years ago due to the impact of a large
asteroid is now widely accepted by scientists and
even a possible site of the impact, off the Yucatan
Peninsula of Mexico, has been identified. Around
65% of species on Earth at that time were killed
off, although it is worth remembering that birds,
direct descendants of the avian dinosaurs, and
more importantly for us, mammals did survive.
A long time before that, around 250 million
years ago there was an even more extreme mass
extinction when over 80% of all species were
eradicated. The extent and causes of this event
are still debated by scientists and may involve
another asteroid as well as huge volcanic eruptions.
Three other large mass extinction events are
known in the last 500 million years of Earth’s
history: The end of the Ordovician Period (440
million years ago), the end of the Devonian
Period (360 million years ago) and the end
of the Triassic Period (200 million years ago)
the change of rocks from limestone to sandstone
and shale. This extinction event is attributed
to changes in climate resulting from the start
of an ice age. This caused changes in sea level,
sedimentation and temperature and some species
were not able to adjust to the new conditions.
Ammonoids, crinoids, conodonts, brachiopods,
foraminifers and corals were all affected. So
as you travel from Black Head to the Cliffs of
Moher or from Corrofin to Ennistymon you are
passing over one of Earth’s mass extinction events.
More recently, many writers are describing a mass
extinction event unfolding on the Earth right now.
A large part of the current mass extinction can be
directly related to the activities of humans due to
deforestation and habitat loss on land. Coupled
with the effects of global warming, in particular
ocean acidification, other effects including the
loss of many marine creatures are inevitable if
current trends continue. Ultimately, if enough of
the ecosystem of the Earth collapses, we could
be willingly participating in our own extinction.
A sixth event, known as the mid-Carboniferous
event (330 million years ago), is also recognized,
and while this wasn’t quite on the same scale as the
other ‘big five’ extinctions, many creatures globally
suffered a serious decline and it is estimated
that around 30% of species were lost at this time.
This extinction event is marked in the Burren in
Article written by Dr. Eamon Doyle, Geologist for
Burren and Cliffs of Moher UNESCO Global Geopark, Clare County Council.
While we like to think that we as humans will
leave a long-lasting legacy on Earth, the processes
of weathering, erosion and plate tectonics would
continue after we are gone and in a relatively short
geological time, there would be virtually zero
trace of our existence in the geological record.
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