Like pulling apart a caramel bar, the earth’s crust was once stretched and thinned out between Europe and North America. This set in motion a process with a warming effect, according to a study: there was an enormous release of the greenhouse gas carbon dioxide around 56 million years ago. According to the researchers, this has probably led to one of the strongest known global warming events in Earth’s history: the Paleocene/Eocene temperature maximum.
It is well known that what we are struggling with today has to do with a man-made cause – but in principle climate changes were not unusual in the history of the earth. A particularly striking episode took place about 56 million years ago. Geological findings show that the global average temperature of the earth’s atmosphere rose by five to eight degrees Celsius in a comparatively short time. This period is referred to as the Paleocene-Eocene Thermal Maximum (PETM) and lasted about 170,000 years. The rise in temperature and the associated climate effects changed the habitats of the earth significantly. This is also reflected in a clear influence on the course of evolution.
Because of the rapidity and magnitude of the warming, the PETM event is often compared to today’s climate change. What was the cause 56 million ago is still unclear. “Despite the far-reaching relevance of the PETM event for today’s global change, the underlying cause is very controversial,” says Tom Gernon University of Southampton. “There is only general agreement that a sudden and massive release of the greenhouse gas carbon dioxide from the Earth’s interior was the cause of this event. But the extent and speed of warming are difficult to explain by conventional volcanic processes,” says the scientist.
Geological causal research
To unravel the causes of the PETM event, Gernon and his international team targeted a geological region that may have played a crucial role in its development: the North Atlantic. Because at the time in question, the area that once united North America and Greenland with Europe was particularly strongly stretched by plate tectonic forces. Through this process, the continental plates eventually separated, resulting in the formation of the North Atlantic. As part of their study, the researchers first examined geochemical analyzes of the relevant layers from rock cores taken from the seabed in the North Atlantic.
They report that studies of the rock strata revealed that the PETM era saw a particularly abrupt and intense increase in volcanic activity in the North Atlantic. According to the findings, this amplification lasted for around 200,000 years – which fits exactly with the previous findings on the course of the PETM. These results then led the scientists to study rocks in an even wider area of the North Atlantic – including Greenland and the Faroe Islands.
Greenhouse gas bubbled out of stretch areas
They found that lava accumulations several kilometers thick, which formed just before the PETM, have an unusual composition. The scientists explain that the characteristics reflect a significant increase in melting processes in the uppermost, solid part of the mantle under the continental plate. “This finding is significant because we know that parts of the continental mantle in this region are enriched with carbonates, an important source of carbon,” says Gernon. “This rapid increase in mantle melt that is now emerging has likely released a very large amount of carbon.” His colleague Thea Hincks goes on to say: “Using physically realistic estimates of the main features of these volcanic systems, we show that the amount of carbon required for warming could have been achieved with increased melting,” says the scientist.
According to the team, the results now paint a possible picture of the process that caused the PETM event: The root cause was the strong stretching of the continental plates in the northern hemisphere – comparable to pulling out a caramel bar, which becomes thinner and eventually breaks apart This process resulted in a massive reduction in pressure at depth in the area. According to the researchers, this was accompanied by an intense but short-lived meltdown in Earth’s mantle — a layer of sticky, molten rock just below the Earth’s crust. The resulting volcanic activity was then accompanied by a massive release of carbon into the atmosphere, which probably led to the warming under the PETM, the scientists conclude.
Source: University of Southampton, professional article: Nature Geoscience: 10.1038/s41561-022-00967-6