Extinction
The history of life on Earth is a long and complex story. Across billions of years we can trace the evolution of simple, single-celled organisms into larger, more complex lifeforms. Using the fossil record, palaeontologists observe the appearance – and disappearance – of lifeforms over time. Surviving on Earth has not always been easy; sometimes things happen that make it hard for animals and plants to continue to exist.
Only koalas can make another koala. If, for some reason, we were to run out of living koalas, then there can be no more: the species becomes extinct. The extinction of plants and animals species can – and does - happen at any time but when it happens to a number of species at once, we call it an extinction event. Palaeontologists studying the fossil record have identified five distinct episodes in time where a great many species, both animal and plant, have suddenly disappeared from the record. These are known as large extinction events or mass extinctions and their effects reset the living world, changing the course of evolution and marking the beginning of new geological periods.
Mass extinctions and their causes are an area of active scientific study. The further back in the geological record an event happened, the more difficult it can be to identify and understand its causes. One thing that these events do seem to have in common, however, is that they involve large changes that happen fast – too fast for life’s systems to be able to adapt.
Three mass extinction events are known to have occurred during the period of time covered by Before the Mountain Had a Name:
Only koalas can make another koala. If, for some reason, we were to run out of living koalas, then there can be no more: the species becomes extinct. The extinction of plants and animals species can – and does - happen at any time but when it happens to a number of species at once, we call it an extinction event. Palaeontologists studying the fossil record have identified five distinct episodes in time where a great many species, both animal and plant, have suddenly disappeared from the record. These are known as large extinction events or mass extinctions and their effects reset the living world, changing the course of evolution and marking the beginning of new geological periods.
Mass extinctions and their causes are an area of active scientific study. The further back in the geological record an event happened, the more difficult it can be to identify and understand its causes. One thing that these events do seem to have in common, however, is that they involve large changes that happen fast – too fast for life’s systems to be able to adapt.
Three mass extinction events are known to have occurred during the period of time covered by Before the Mountain Had a Name:
The Great Dying (End-Permian Extinction)
252 million years ago something happened that killed a greater proportion of animal and plant species than any other event before or since (so far). Known as the Great Dying, this event now marks the end the Permian period, setting the world on course for the Age of Dinosaurs.
Evidence from fossils, rock chemistry and geology shows that the Great Dying coincided closely with a Large Igneous Province (LIP) event, the eruption of the Siberian Traps. Thought to be a result of processes that may also cause the break-up of continents, LIP events are enormous volcanic eruptions that happen all at once over a wide geographical area. In Siberia between 5 -7 million square km of land were covered by an estimated 4 million cubic kilometres of mainly basaltic rocks. Analysis of chemical isotopes within the basalts show that this all happened within a relatively short geological time – only one or two million years.
Such large volcanic eruptions would have released equally large volumes of volcanic gases, sulphur and carbon dioxide into the atmosphere, affecting both climate and ocean chemistry. Debate continues about whether the eruptions alone are sufficient to account for the changes observed. Some geologist theorise that the volcanic event burned thick sequences of coal present in the area of eruption, releasing huge volumes of carbon dioxide in addition to the volcanic gases.
Evidence from fossils, rock chemistry and geology shows that the Great Dying coincided closely with a Large Igneous Province (LIP) event, the eruption of the Siberian Traps. Thought to be a result of processes that may also cause the break-up of continents, LIP events are enormous volcanic eruptions that happen all at once over a wide geographical area. In Siberia between 5 -7 million square km of land were covered by an estimated 4 million cubic kilometres of mainly basaltic rocks. Analysis of chemical isotopes within the basalts show that this all happened within a relatively short geological time – only one or two million years.
Such large volcanic eruptions would have released equally large volumes of volcanic gases, sulphur and carbon dioxide into the atmosphere, affecting both climate and ocean chemistry. Debate continues about whether the eruptions alone are sufficient to account for the changes observed. Some geologist theorise that the volcanic event burned thick sequences of coal present in the area of eruption, releasing huge volumes of carbon dioxide in addition to the volcanic gases.
The End-Triassic Extinction
The end of the Triassic period is marked by another mass extinction event, although this one isn’t mentioned in the book. Not as devastating as the Great Dying (in terms of the number of species lost) this event may also have been related to a LIP event – in this case the Central Atlantic Magmatic Province that preceded the opening of the Atlantic Ocean and the break-up of Pangaea.
The Extinction of the Dinosaurs (End-Cretaceous Extinction)
The most well-known (and arguably the best understood) mass extinction event is that which resulted in the end of the Age of Dinosaurs. This event is most likely to have been triggered by a large meteor impact in what is now the modern Gulf of Mexico. Estimated to have been caused by an asteroid around 12km wide, the effects of this collision were both sudden and dramatic. Scientists debate whether or not a devastating global firestorm may have occurred post-impact but most agree that material ejected into the atmosphere would have blocked sunlight all around the world for several years, causing plants to die and global temperatures to drop.
