Mass extinction events spanning two global warming periods in Earth’s history wiped out huge amounts of ocean life and destroyed reef ecosystems, a new study warns.
It’s previously been suggested that the Late Triassic and Early Toarcian extinctions, both linked to massive volcanism and the resulting climate changes, simply intensified extinction rates that were already underway.
But according to new research, this was not the case.
An analysis of background extinction rates and those experienced during the two events suggests extinction patterns changed dramatically each time due to rising ocean temperatures, acidification, and oxygen-starved waters.
The Late Triassic mass extinction (LTE) and the Early Toarcian (ETOE) extinction took place about 201 million years ago and 187 million years ago, respectively.
The latter is considered the second largest marine biodiversity loss event in Earth’s history.
According to the new research, these past warming periods and the resulting extinctions offer a glimpse at the threats posed by human-induced climate change today.
Both of these events were ‘responsible for the mass extinction of marine organisms and resulted in significant ecological upheaval,’ the paper notes.
The team modelled extinction through the Late Triassic and Early Jurassic using a global database of marine organisms.
And, this revealed profound changes that varied between the two extinction events.
Both periods experienced changes in extinction selectivity – or the types of species going extinct during that time – but the effect was more extreme during the Late Triassic.
This finding goes against the previous suggestion that there were no differences in extinction selectivity from the background rates.
The team also found some patterns that arose between the two separate events.
‘Despite differences in starting conditions, species involved, and magnitudes of global warming and environmental change, the LTE and EToE show some common patterns of selectivity,’ the researchers explain in the study.
‘Both events record strong extinction selectivity against pelagic predatory guilds and against benthic photosymbiotic and suspension feeding organisms, suggesting that these groups of marine organisms may be particularly vulnerable during episodes of global warming.’
WHEN WERE EARTH’S ‘BIG FIVE’ EXTINCTION EVENTS?
Traditionally, scientists have referred to the ‘Big Five’ mass extinctions, including perhaps the most famous mass extinction triggered by a meteorite impact that brought about the end of the dinosaurs 66 million years ago.
But the other major mass extinctions were caused by phenomena originating entirely on Earth, and while they are less well known, we may learn something from exploring them that could shed light on our current environmental crises.
- The Late Ordovician: This ancient crisis around 445m years ago saw two major waves of extinction, both caused by climate change associated with the advance and retreat of ice sheets in the southern hemisphere. This makes it the only major extinction to be linked to global cooling.
- The Late Devonian: This period is now regarded as a number of ‘pulses’ of extinction spread over 20m years, beginning 380m years ago. This extinction has been linked to major climate change, possibly caused by an eruption of the volcanic Viluy Traps area in modern-day Siberia. A major eruption might have caused rapid fluctations in sea levels and reduced oxygen levels in the oceans.
- The Middle Permian: Scientists have recently discovered another event 262m years ago that rivals the ‘Big Five’ in size. This event coincided with the Emeishan eruption in what’s now China, and is known to have caused simultaneous extinctions in the tropics and higher latitudes.
- The Late Permian: The Late Permian mass extinction around 252m years ago dwarfs all the other events, with about 96% of species becoming extinct. The extinction was triggered by a vast eruption of the Siberian Traps, a gigantic and prolonged volcanic event that covered much of modern day Siberia, which led to a cascade of environmental effects.
- The Late Triassic: The Late Triassic event, 201m years ago, shares a number of similarities with the Late Permian event. It was caused by another large-scale eruption, this time of the Central Atlantic Magmatic Province, which heralded the splitting of the supercontinent Pangaea and the initial opening of what would later become the Atlantic Ocean.
According to the researchers, both of the warming events triggered rapid temperature increases, ocean anoxia (in which oxygen is depleted), and acidification.
This, in turn, led to the collapse of reef ecosystems.
In addition to uncovering new clues on Earth’s past, the researchers say the findings provide ‘ample warning’ about what could arise as a result of current climate change trends.