The ending of the Permian period 252 million years ago gave way to the Mesozoic era - more
popularly known as the ‘Age of the Dinosaurs’.
The Mesozoic - made up of the Triassic, Jurassic and Cretaceous Periods - saw the evolution
of all sorts of iconic animals, and in many ways it was during this Era of time that the
world we know today found its beginnings.
The first mammals, birds, lizards, snakes, turtles and many modern amphibian groups all
originated during this massive stretch of Deep Time.
However, the start of the Mesozoic was a time of great upheaval and unimaginable devastation,
as the boundary between the Permian and the Triassic also marked the most severe mass
extinction event in the history of life on Earth - the imaginatively named Permian Triassic
Mass Extinction, or, more dramatically; The Great Dying.
Now, I’ve actually been lucky enough to stand on this boundary itself, back when I
was invited to join an expedition in South Africa to search for fossils in the Karoo
semi-desert.
The feeling of standing on this divider was a profound one, knowing how much carnage and
death these rocks represented, and despite it all happening over 250 million years ago,
I couldn’t help but feel a little sad for all the magnificent species that were wiped
from the face of our world.
Estimates for the severity of this event vary, with some studies putting the extent of marine
species extinction at about 81%, whereas others put it at an even more extreme 94%.
The four-legged, backboned inhabitants of the land at this time - the tetrapods, which
includes our own ancestors - may have experienced an 89% loss of genera over the last million
years of the Permian period, and it was also only the second ever mass extinction of plants,
as well as the only mass extinction to have severely affected insects.
There also appear to have been distinct pulses of extinction, with different timings of extinction
for terrestrial and marine organisms.
Although the specifics are still debated, it seems as though the terrestrial extinction
occurred sooner than the marine one, and that stresses to the marine environments happened
first in higher latitude regions, before the lower latitudes.
So, there’s no denying that this was a truly terrible time to be alive, and the odds for
a lot of animals around at this time were that they would not be making it through to
the following Triassic Period.
Indeed, the tetrapods living on the land before the extinction event were very different to
the ones found after, and the terrestrial ecosystems of the planet - which had been
dominated by groups of animals related to our ancestors, called synapsids - would eventually
give way to the crocodile relatives and, of course, the dinosaurs.
A total restructuring of vertebrate life on land happened after this extinction, and the
planet was never the same again.
So why did the P/T extinction wipe out so much of the life that inhabited this Permian
world?
Why was the Great Dying quite so bad?
Well, it has a lot to do with the specific geological conditions of the volcanism considered
responsible for this destruction.
It was first noticed in the 1990s that there might be a potential link between this notable
decline in diversity of various groups and the rapid eruption of incredibly widespread
flood basalts in Siberia, which occurred at around the same time.
These flood basalts, which are still clearly visible today in eastern Siberia, are the
result of a huge volume of lava spreading over the surface of the Permian earth as a
‘Large Igneous Province’ - a so-called LIP - became emplaced.
What this means is that a massive amount of igneous material quite quickly rose to the
surface of the Earth over a very wide area, resulting in both intrusion - with the magma
being forced into rocks underground and melting them - as well as extrusion, finding its way
to the surface and spreading out as lava.
Well, there appears to be somewhat of a correlation between the formation - or emplacement - of
these LIPs and some of the major mass extinctions throughout the history of life on our planet.
It’s not always a perfect, clear cause-and-effect relationship however - but in the case of
the end Permian extinction all the current evidence points to the Siberian Traps Large
Igneous Province as being the main driver of the destruction.
But if LIPs have been the cause of at least some other mass extinctions too, what made
the Siberian ones quite so deadly?
That’s where the geology of the region this volcanism happened in comes into play.
Millions and millions of years earlier, huge volumes of evaporating water left behind mineral
deposits called - unsurprisingly - evaporites.
These evaporite deposits were then covered by successions of sediment over millions of
years, being buried far underground.
In addition to these evaporites, there were also layers of sediment that were particularly
rich in concentrated organic material.
So why is this important?
As it turns out, the presence of these deposits was a complete disaster for life on Earth
when the LIP started to come into contact them.
3 different phases of activity have been identified as having happened when the Siberian Traps
formed.
The first stage, beginning just before about 252.24 million years ago, involved a lot of
extrusive and explosive volcanic activity, with a lot of pyroclastic eruptions as well
as incredible volumes of lava pouring out onto the surface.
Now, you might imagine that this would have a pretty devastating impact on the planet
- and indeed, any living things in the vicinity of these eruptions would have been getting
pretty toasty, and there is some evidence for changes in the carbon cycle, as well as
peaks in concentrations of Mercury in the sediments layed down at this time - an unmistakable
signal of increased volcanism - at a site in Canada.
However, there seems to have been less of an effect on global conditions at this time
than we might have expected.
It’s at about this time that the earlier terrestrial extinction we talked about before
seems to have been occurring, and the mass extinction of plants was taking place - one
of only two mass plant extinctions to have happened in the history of their evolution.
There seems to have been a lot of stress on the terrestrial ecosystems at this time, resulting
in their eventual collapse and turnover.
However, the marine realm was still largely unaffected by these events.
But even more destruction was still on the way, and the marine life of the Permian would
soon get its fair share of the extinction.
The second stage of the Siberian Traps emplacement started around 251.9 million years ago, after
about 300,000 years of Stage 1 eruptions.
This second phase was very interesting - the extrusive eruptions of vast quantities of
lava onto the surface stopped, and instead extensive underground complexes of magma were
forced in between the sedimentary layers that made up the rock here.
This is where everything went south for the marine organisms of the Permian.
When the magma intruded into the sedimentary rocks under the surface, they came into contact
with those evaporite and organic-rich deposits - and disaster followed.
Due to the effects of contact metamorphism, vast quantities of gases - specifically, halocarbons
and greenhouse gases - were mobilised from these deposits, and escaped to the surface
as evidenced by pipe and vent structures that indicate these gases violently exploded up
from underground and into the atmosphere.
Once they’d been released, havoc was unleashed upon the environment.
Halocarbons are associated with ozone depletion, and so the vast quantities of these gases
in the Permian atmosphere likely brought about the collapse of the ozone layer, while the
greenhouse gases released from the organic-rich rocks (carbon dioxide and methane) would have
resulted in global climate change, including rising temperatures, acidification of the
oceans and widespread oceanic anoxia.
This is when the marine extinction happened - the worst marine extinction of the past
half a billion years.
The last of the Trilobites were wiped from the face of the planet, along with many other
groups of not quite so well-known organisms as conditions in the ocean all across the
planet deteriorated - the world would forever be a changed place after this event.
The third stage of Siberian Traps activity then began around 251.48 million years ago,
and was characterised by a continued intrusion of magma underground, as well as a resumption
of lava being erupted onto the surface - however, records of Carbon isotopes from this time
indicate that they began to return back to pre-extinction levels, suggesting some recovery
of environmental conditions.
Although many details of the Permian-Triassic Mass Extinction event are still heavily debated,
and the timings of when different organisms died out as well as exactly when various volcanic
events occurred are the subject of a great deal of discussion, it seems quite apparent
that the excessive severity of the Great Dying has a lot to do with the underlying geology
of the Siberian Traps.
It’s quite alarming to think that the history of life on our planet could have been entirely
different if it weren’t for the specific region the Siberian Traps formed in and making
this such a destructive extinction.
The world could have remained a very different place - but, luckily for us at least, those
good old evaporites and organic-rich deposits changed the course of evolutionary history.
The Great Dying also has some very serious and quite worrying lessons for our future,
too.
The release of vast quantities of greenhouse gases and depletion of the ozone layer are
all too familiar threats to our modern world, and the fact that such dramatic consequences
can be seen in the record of past life on Earth really should be of concern to humans
as a species.
And then there’s the fact that the change in global temperatures at the end of the Permian
were actually happening at a much slower rate than what we see today, which is a pretty
terrifying prospect.
But that just goes to show the importance of palaeontology as a science, and its relevance
to us today.
The past really is the key to the present, sometimes.
Anyway, I really hope you enjoyed watching this video.
This was actually inspired by some coursework I had to do for my university degree, in which
I undertook a literature review on the use of proxies for the Permian Triassic Mass Extinction,
and so I thought I may as well link to that in the description below in case anyone wanted
to read it and maybe decide what grade I should get for it, I don’t know.
I just enjoyed reading about our current understanding of this event and realising that there’s
still a lot that needs to be found out
about it.