In last month’s blog we took a brief look at the local and global effects of an asteroid impact on the Earth. This month we look at when mass extinction events have occurred within geological time, their relative effects and their correlation to known asteroid impacts. We will discuss the possible causation of the latter to the extinction event(s).
Le mois dernier nous avons considéré les effets locaux et mondiaux d’un impacte d’astéroïde sur la Terre. Ce mois nous allons considérer leurs effets relatifs; quand se sont déroulés ces événements au cours des temps géologiques, et la corrélation entre ces événements et les impactes d’astéroïdes connus.
Mass extinctions over geological time.
Throughout geological history species have arisen and disappeared. The causes of a species going extinction can be many; ranging from, for examples; disruption to their food chain; predator dominance; fertility reductions; disease susceptibility; failure to adapt to evolving environmental conditions and habitat changes; and large scale vulcanism.
Throughout geological history species have arisen and disappeared. The causes of a species going extinction can be many; ranging from, for examples; disruption to their food chain; predator dominance; fertility reductions; disease susceptibility; failure to adapt to evolving environmental conditions and habitat changes; and large scale vulcanism.
Tout au long de l’histoire géologique, des espèces sont apparues et ont disparu. Bien des raisons peuvent expliquer la disparition d’une espèce: par exemple la rupture d’une chaîne alimentaire; l’existence de prédateurs; une baisse de fécondité, la vulnérabilité aux maladies; l’incapacité de s’adapter à de nouveaux conditions environmentales; et le volcanisme à grande échelle
There are also more ‘cosmological’ causes as to why life forms may be eradicated. These include destruction of the ozone layer leading to high doses of ultraviolet radiation; high energy solar x-ray flares directed towards to Earth; nearby supernova generating high levels of gamma wavelength radiation; and comet or asteroid collisions. Of these, the collisions are expected to be the most frequent.
(Note – the climate change we are currently experiencing on Earth is often cited by those who dispute the anthropological nature of these as being a realisation of the Milankovitch cycles of the Earth’s orbit. This is wholly incorrect and based on a complete lack of understanding of the latter). We address this partly in our article on Ice and Climate change although it seems we may need to write a more detailed description of the Milankovitch processes to dispel the damaging conspiracy theory.)
(Note – the climate change we are currently experiencing on Earth is often cited by those who dispute the anthropological nature of these as being a realisation of the Milankovitch cycles of the Earth’s orbit. This is wholly incorrect and based on a complete lack of understanding of the latter). We address this partly in our article on Ice and Climate change although it seems we may need to write a more detailed description of the Milankovitch processes to dispel the damaging conspiracy theory.)
Biological genera losses over geological time
This diagram shows the percentage of extant biological genera lost (the y-axis, units are %) mapped against geological time eras. The x-axis, units are millions of years before now, and at the top, the abbreviated name of the geological era. In biological taxonomy, genus (plural is genera) are a subset of family, and comprise a set of species. Sadly, it now seems evident that we are undergoing another period of mass species extinction. This has been precipitated by predominately habitat changes and other anthropological causes.
Asteroid/Comet Impact correlation to mass species extinction events.
The table below shows the time frame of major asteroidal impacts (defined here as one which produces a crater > 25km in diameter) over the last 500 million years, in comparison to the timeframe of mass extinction events (where at least 20% of all biological genera become extinct).
Asteroid/Comet Impact correlation to mass species extinction events.
The table below shows the time frame of major asteroidal impacts (defined here as one which produces a crater > 25km in diameter) over the last 500 million years, in comparison to the timeframe of mass extinction events (where at least 20% of all biological genera become extinct).
Correlation of mass extinction events to asteroid/comet impacts
We can see from this comparative table that the only impacts closer than 4 million years in time to a mass extinction event are the Rochechouart and the Chicxulub strikes. The link between Chicxulub and the extinction of the dinosaurs has been well researched and popularised. The coincident Limousin impact to the Rhaetian age extinction has been less researched and promoted.
The table shows that whilst Chicxulub and Rochechouart are coincident with mass extinctions, it’s clear that mass extinctions do not necessarily follow on from a large impact. The Manicouagan impact appears not to have led to a mass extinction (although it should be noted this is ‘definition’ dependent; about 10% of genera became extinct at the same time as the Manicouagan event).
Conversely, there appears not to have been any significant asteroid impact within 38 million years of the largest mass extinction ever recorded, the extinction at the end of the Permian period. Our conclusions thus are:
Further reading
The Limousin Asteroid impact of the Triassic Rhaetian age
N Taylor. Observatoire Solaire. 2017. ISBN 978-1-999-904-41-8
https://www.amazon.co.uk/Limousin-Asteroid-Impact-Triassic-Rhaetian/dp/1999904419
Next Month
We will look at the Chelyabinsk and Tunguska events.
The table shows that whilst Chicxulub and Rochechouart are coincident with mass extinctions, it’s clear that mass extinctions do not necessarily follow on from a large impact. The Manicouagan impact appears not to have led to a mass extinction (although it should be noted this is ‘definition’ dependent; about 10% of genera became extinct at the same time as the Manicouagan event).
Conversely, there appears not to have been any significant asteroid impact within 38 million years of the largest mass extinction ever recorded, the extinction at the end of the Permian period. Our conclusions thus are:
- Mass species extinction events can be caused by planetary impact;
- Impacts are not the only causes;
- Impact events can contribute to mass extinction events alongside other causes.
Further reading
The Limousin Asteroid impact of the Triassic Rhaetian age
N Taylor. Observatoire Solaire. 2017. ISBN 978-1-999-904-41-8
https://www.amazon.co.uk/Limousin-Asteroid-Impact-Triassic-Rhaetian/dp/1999904419
Next Month
We will look at the Chelyabinsk and Tunguska events.
