Mass Extinction


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)

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 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.

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.


Dr. Eamon Doyle, geologist for the Burren and Cliffs of Moher UNESCO Global Geopark.