What is Paleocene Eocene Thermal Maximum?
In order to understand what the Paleocene Eocene Thermal Maximum is, it is necessary to know about the Paleocene Eocene Epochs.
Paleocene Epoch: The Paleocene Epoch is a geological time-scale that lasted from 66 to 56 million years ago. This was the time of dinosaurs and is famously marked for the extinction event of non-avian dinosaurs because of an asteroid impact, along with 75% of living species. The end of the epoch is marked by Paleocene Eocene Thermal Maximum.
Eocene Epoch: The Eocene Epoch is the geological time-scale that lasted from 56 million years ago i.e. the end of Paleocene Epoch, to 33.9 million years ago i.e. the beginning of Oligocene Epoch.
Paleocene Eocene Thermal Maximum (PETM): It is a time period in the geological history of Earth when there was globally more than 5℃ - 8℃ temperature rise across the Earth. It is also known as initial Eocene Thermal Maximum 1 (ETM).
Characterising Paleocene Eocene Thermal Maximum
Towards the end of the Paleocene Epoch and the beginning of Eocene Epoch there was a temperature rise of 5℃ - 8℃ globally. The temperature rise was observed across the event which lasted from 20,000 to 50,000 years. The entire period was warm and has been known for increased temperature for approximately 2,00,000 years. The exact age and the duration of the event is arguable but has been estimated to have begun and occurred around 55 million years ago, the boundary of Paleocene Eocene Epochs.
The starting of the Eocene Thermal Maximum has been said to have occurred because of the increased volcanic activity or volcanism and the uplift that is associated with the North Atlantic Igneous Province (a large area in north atlantic region centered on iceland) that lead to significant changes in the carbon cycle of Earth which in turn lead to the global temperature rise of 5℃ - 8℃. The period is marked by the high decrease observed in the amount of 13C stable isotope of carbon all over the world. This led to the decrease of the 13C/12C ratio of marine and terrestrial carbonates and organic carbon. From the combined data obtained of isotopes, 𝛿13C, 𝛿11B, 𝛿18O it is observed that approximately 12,000 Gigatonnes of carbon was released into the atmosphere for a period of 50,000 years, with 0.24 Gigatonnes per year average. This means that at least 44,000 Gigatonnes of carbon dioxide responsible for global warming was released into the atmosphere due to extreme geological events.
Changes During Paleocene Eocene Thermal Maximum
Apart from the rise in the carbon dioxide levels due to volcanic activity throughout the globe, there were several other changes that led to drastic changes in the animal and plant life both on land and in the ocean. These other changes are observed by the stratigraphic sections of the rock from this period that reveal numerous changes.
Many of the fossil records show major and significant changes and turnovers in the profile of organisms over the Earth. Examples include the changes in the marine realm, there was a mass extinction of the benthic foraminifera and a global expansion of the subtropical dinoflagellates. There was also an appearance of increase in the population of the planktic foraminifera and calcareous nannofossils. All these were observed during the beginning stages of PETM. The mammalian sea-animals also sprung and got the advantage of the wide resources available to them. There is trace evidence of the impacts of the rising temperatures and increase in the carbon dioxide content of the atmosphere leading to decrease in the amount of dissolved oxygen in the oceanic water, in turn affecting the life of deep-sea species. But one specific development is known about the increase in the population of heavily calcified algae and weakly calcified forams which occurred due to acidification of the water bodies.
Similar things were observed on land as well. The modern mammalian order including the primates suddenly appeared in the continents of Europe and North America. There is a widespread migration known for Asian mammals towards the north, because of the prevailing humid conditions. Also, the population of the mammalian species increased many fold during this time. Increase in the levels of CO2 may have facilitated the physical trait of dwarfing in turn encouraging speciation. Some 13,000 to 22,000 years after the initiation of the PETM, many animals belonging to the mammalian orders such as Artioctyla, horses and primates spread around the globe. The deposition of the sediments also changed the outcrops and many of the drill cores that spanned the time interval.
Recovery and Comparison With Current Global Warming
In order to understand the climatic conditions of olden times such as the Paleocene Epoch about 56 million years ago, climate proxies are used. Climate proxies are the preserved physical characteristics of the past, that show us visible proof and help us understand and reconstruct the possible behaviour of the climate during that time. From such climate proxies it is stated that the recovery might have occurred with an increase in the biological productivity. Increased biological productivity might have helped to form an appropriate carbon cycle and would have transported carbon to the deep oceans. This would have occurred with higher global temperatures, higher CO2 levels, and increased supply of nutrients from continental weathering (because of higher temperatures and higher rainfall) and depositions from volcanic eruptions.
The evidence of such an increased biological productivity leading to recovery is given by the bio-concentrated barium. But there is a possibility that the bio-concentrated barium may have been because of barium dissolved with methane which is a later event and a possibly recent event. The diversification of the plant species, especially the ones near the shores indicate that productivity increase in such areas as the weather there would have been warm and fertilized run-off which had outweighed the reduction of productivity in the deep ocean areas.
The initial Eocene Thermal Maximum 1 has been the centre point of investigation as an analog to understand the effects of global warming. Although, the adverse effects of global warming and the reason are much worse today as compared to the period of PETM. Humans emit 10 Gigatonnes of carbon dioxide into the atmosphere as compared to the 0.24 Gigatonnes produced per year during PETM. Another difference is that during the PETM the planet was ice-free and the effects of global warming on such areas isn't clear but the effects will be known by today as the water level rises all over the world due to melting glaciers and melting ice at the poles. Also, it is said that the cause of the PETM were the widespread volcanic eruptions and the K-T extinction event but they are still debatable and the cause, details and the overall significance of the event remain uncertain. It has already been established that the peak carbon addition to the ocean-atmosphere system during the PETM is much slower and lower than the carbon addition by human activities. Also, it is said that the current methane emission regime is similar to the one that occurred during the PETM. Thus, it is understandable what such emissions can lead to and the changes and impact that it can have on the species life and nature.
FAQs on Paleocene-Eocene Thermal Maximum
1. What exactly was the Paleocene-Eocene Thermal Maximum (PETM)?
The Paleocene-Eocene Thermal Maximum (PETM) was a period of intense and rapid global warming that occurred approximately 56 million years ago. It marks the boundary between the Paleocene and Eocene epochs. This event was characterized by a massive release of carbon into the atmosphere and oceans, leading to a global temperature increase of 5 to 8°C in a relatively short geological timeframe.
2. What were the primary causes of the PETM?
While the exact trigger is debated, the leading theory is the massive injection of carbon into the Earth's systems. Potential sources for this carbon release include:
- Widespread volcanic activity releasing large amounts of carbon dioxide (CO2).
- The melting of methane hydrates (frozen methane deposits) from the ocean floor, which released vast quantities of methane, a potent greenhouse gas.
- The burning of extensive peat and coal deposits.
3. How did the PETM affect life and ecosystems on Earth?
The PETM caused significant ecological changes. In the oceans, it led to widespread ocean acidification and anoxia (lack of oxygen), causing a major extinction event for deep-sea benthic foraminifera. On land, the warming led to major shifts in flora and fauna, including the migration of animals towards the poles. It also spurred the rapid evolution and diversification of many modern mammal groups, including primates.
4. What was the role of carbon dioxide (CO2) during the PETM?
Carbon dioxide (CO2), along with methane, was the primary driver of the warming during the PETM. Geochemical evidence from ancient soils and marine fossils suggests that atmospheric CO2 concentrations likely rose from around 1,000 parts per million (ppm) to over 2,500 ppm. This dramatic increase in greenhouse gases trapped heat in the atmosphere, causing the significant rise in global temperatures.
5. Is the PETM considered a mass extinction event?
The PETM is not classified as one of the 'Big Five' mass extinction events, like the one that killed the dinosaurs. While it caused a severe extinction event in the deep ocean (affecting 30-50% of benthic foraminifera), life on land and in surface waters adapted, migrated, or evolved in response to the changes. It was more of a period of major biological turnover and reorganisation rather than a catastrophic mass extinction across all environments.
6. Why is studying the PETM important for understanding modern-day climate change?
The PETM serves as a crucial historical analogue for today's anthropogenic climate change. It demonstrates how a rapid, large-scale release of carbon can dramatically alter global climate, ocean chemistry, and ecosystems. By studying the PETM's causes, effects, and the Earth's eventual recovery, scientists can better model the potential long-term consequences of our current carbon emissions and understand the planet's climate sensitivity.
7. How does the rate of carbon release during the PETM compare to current emissions?
This is a key point of comparison. While the total amount of carbon released during the PETM was immense, it occurred over several thousand years. In contrast, current human-caused carbon emissions are releasing carbon into the atmosphere at a rate that is estimated to be nearly ten times faster than the rate during the PETM. This unprecedented speed presents a unique and potentially more severe challenge for modern ecosystems to adapt to.
8. How did the Earth eventually recover from the PETM?
The Earth's recovery from the PETM took a very long time, estimated to be around 150,000 to 200,000 years. The excess carbon was slowly removed from the atmosphere and oceans through natural geological processes. This primarily involved the weathering of silicate rocks on land, which draws down CO2, and the burial of organic carbon in ocean sediments. The recovery highlights the very slow pace of natural carbon sequestration compared to the rapid pace of its release.
