Think of a volcanic eruption – Vesuvius, say, or Krakatoa. Double it. Treble it. Keep on multiplying it. Oh, never mind – just imagine a volcanic eruption so huge that it covers thousands of square kilometres and lasts for thousands, sometimes millions, of years. Now you’re beginning to grasp the scale and extent of the generation of a flood basalt province.
It may seem like the stuff of science fiction (and highly improbable science fiction at that) but in fact, such mind-bogglingly large volcanic events have played a repeated part in the creation of the earth as we know it – not only shaping topography (they underlie such areas as India’s Deccan Traps, the Columbia River Plateau in the north-western USA and large parts of Antarctica) but also in establishing and altering the composition of the planet’s flora and fauna – and they may have also contributed to the demise of the dinosaurs.
Along with new land (Self and Rampino estimate that some may have generated two million cubic kilometres of lava) such eruptions created enormous volumes of gas. There are no clear figures, but estimates suggest that a single flow from the Columbia River eruption alone would have produced approximately 1.3 x 1013 kg of sulphuric acid aerosols and released enormous quantities of other gases, including carbon dioxide, into the atmosphere – causing major changes to global climate.
Mass Extinctions and Their Causes
Throughout the Earth’s history, mass extinctions have taken place – that is, the extinction of large groups of organisms in very short time periods. These are identified by the sudden disappearance of these groups from the geological record. Typically, they occur at the end of geological time periods known as stratigraphic boundaries.
The most notorious mass extinction is that of the Late Cretaceous, around 65 Ma, or 65 million years ago (The term Ma is short for “megaannum”, or one million years), during which the reign of the dinosaurs ended on Earth. In addition, geologists recognise four other major episodes of mass extinction and several lesser ones. The five major extinctions are:
- Late Ordovician, which occured around 440 Ma.
- Late Devonian, which occuredaround 365 Ma.
- Late Permian, which occured around 248 Ma.
- Late Triassic,which occured around 210 Ma.
- Late Cretaceous,which occured around 65 Ma.
These affected different groups of species (the Devonian extinction, for example, was particularly devastating to marine creatures). Some lasted millions of years and included more than one peak of extinctions. While no definitive single cause has been attributed to any one of them, they are generally associated with periods of catastrophic climate or other environmental change.
Clearly, massive eruptions on the scale of some flood basalts can be considered to be just such catastrophic environmental events. There are other events, however, which also fall into this category. These include meteorite impacts (major impacts are thought to be contemporaneous with both the Late Cretaceous and Late Triassic events) and glaciations (associated with the Late Ordovician).
Flood Basalts and Mass Extinctions
Because flood basalt events took place so far in the geological past (only one, the Laki fissure eruption, has taken place in the period of recorded history and the most recent major event, the Columbia River eruption, is dated at around 17 million years ago) much information about their impacts remains conjectural.
Earth scientists Steve Self and Mike Rampino listed major known flood basalt eruptions alongside mass extinctions (major and lesser), producing interesting results. Many occur relatively closely in terms of (geological) time. Three eruptions correlate extremely closely to major extinctions – the Deccan with the Late Cretaceous, Newark with the Late Triassic, and Siberian with the Late Permian. On this basis, some geologists argue that flood basalts are a cause of mass extinctions.
On the other hand, other geologists argue a case for major impact events: the identification of a major impact crater contemporaneous with the Late Cretaceous mass extinction is the basis for the current theory. The theory that it was this extra-terrestrial event which caused the death of not only the dinosaurs but many other species, is taught as fact to almost every schoolchild.
Flood Basalts: Did They Help Kill the Dinosaurs?
That there was an impact at the end of the Cretaceous period is not in question: nor is the fact that the Deccan flood basalt event was occurring at the time of that impact. Both events would have had significant environmental impacts in terms of generating vast quantities of dust and atmospheric material, contributing to such issues as climate change, loss of vegetation and changes in ocean chemistry.
Mass extinctions cannot, at present, be attributed to a single cause, but may have resulted from different sorts of environmental disturbances. In the case of the dinosaurs, it seems that there was a coming together of two such events – although whether either was sufficient, or the extinction was the result of both combined, cannot be said for certain.
Sources and Further Information
Allaby, A., Allaby, M. (eds) Oxford Dictionary of Earth Sciences. Oxford University Press. 1999.
Angela Colling et al. Earth and Life. The Open University. 1997.
Michael R Rampino Mass extinctions of life and catastrophic flood basalt volcanism. Accessed 21 September, 2011.
Self, S., Rampino, M. Flood Basalts, Mantle Plumes and Mass Extinctions. The Geological Society. Accessed 21 September, 2011.
This article was first published on Suite 101.