Sign In
New Zealand; International
Media release
From:
New evidence changes key ideas about Earth’s and climate history
A new study published in Science resolves a long-standing scientific debate, and it stands to completely change the way we think about Earth, evolution, and climate.
The research debunks the idea that Earth’s surface (across land and sea) has experienced really hot temperatures over the last two billion years. Instead, it shows that Earth has had a relatively stable and mild climate.
Temperature is an important control over chemical reactions that govern life and our environment. This ground-breaking work will have significant implications for scientists working on climate models or questions surrounding biological and climate evolution.
“Knowledge of temperatures in the past can help us understand how the Earth’s climate system works and provide insight into the conditions that allowed for the origin and evolution of life,” says University of Waikato geochemist and lead author, Dr Terry Isson.
Understanding past temperatures and the evolution of life is not an exercise in history or pure intellectual curiosity but is vital for understanding future climate. The work underpins the modelling of present-day climate.
“We can’t use our planet as a large-scale lab to understand how the Earth works. Looking to the past provides a way to understand the processes that regulate the Earth’s climate.”
In the work Dr Isson and PhD student Sofia Rauzi adopted novel methods to illuminate a history of Earth’s surface temperature.
They utilised five unique data records derived from various rock types including shale, iron oxide, carbonate, silica, and phosphate. Collectively, these ‘geochemical’ records comprise over thirty thousand data points that span Earth’s multi- billion-year history.
To date, the study is the most comprehensive collation and interpretation of one of the oldest geochemical records – oxygen isotopes. Oxygen isotopes are different forms of the element oxygen.
It is also the first study to use all five existing records to chart a consistent ‘map’ of temperature across an enormous portion of geological time.
“By pairing oxygen isotope records from different minerals, we have been able to reconcile a unified history of temperature on Earth that is consistent across all five records, and the oxygen isotopic composition of seawater,” says Dr Isson.
The study disproves ideas that early oceans were hot with temperatures greater than 60°C prior to approximately half a billion years ago, before the rise of animals and land plants. The data indicates relatively stable and temperate early-ocean and temperatures of around 10°C which upends current thinking about the environment that complex life evolved in.
“It also tells us there are naturally occurring processes that tightly regulate temperatures on Earth.”
The work produces the first ever record of the evolution of terrestrial (land-based) and marine clay abundance throughout Earth history. This is the first direct evidence for an intimate link between the evolution of plants, marine creatures that make skeletons and shells out of silica (siliceous life forms), clay formation, and global climate.
“The results suggest that marine clay formation may have played a key role in regulating climate on early Earth and sustaining the temperate conditions that allowed for the evolution and proliferation of life on Earth,” says Dr Isson.
Overall the work provides new evidence of the Earth’s climate and geochemical history that needs to be better understood to inform and update current ideas and research around climate and evolution.
Dr Isson concludes, “The results provide us with an impetus to deepen our understanding of how life both responds to, and shapes climate on Earth.”
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Dr Chris Hollis, Adjunct Professor, School of Geography, Environment and Earth Sciences, Te Herenga Waka Victoria University of Wellington
This is a fascinating new study of ancient climate that compiles an impressive record of geochemical data for 3.5 billion years of Earth history. In a sense, the results are reassuring in that they show that the Earth system has managed to self-regulate temperature and greenhouse gas levels over this immense time period.
"From a personal perspective as a paleontologist who has specialised in the study of silica-shelled plankton, it is affirming to know that these tiny organisms appear to have played a lead role in cooling the planet at least two times in the past 500 million years. However, these are long-term processes that play out over millions of years and may be of less help for dealing with the modern climate crisis. Nevertheless, it will be interesting to see how this research progresses and in particular see how these regulating processes operate over the shorter times scales of the climate events of the Cenozoic, i.e. the last 66 million years, especially the Eocene greenhouse - the last time the planet's atmosphere pushed past 500 ppm CO2.
Dr Giuseppe Cortese, Principal Scientist – Paleoclimate, GNS Science, comments:
This paper provides a robust, multi-billion-year history of Earth’s temperature, offering fascinating insights into the temperature regime prevalent on Earth from its infancy to today. The authors describe how this history is shaped by a variety of processes, including the interplay between the evolution of life forms (including plants), sites of formation and alteration of sediments, and a series of feedback loops that either amplify or dampen changes.
The study suggests that, during the time interval older than ca. 500 million years, temperatures on Earth ranged between 2 and 46°C. These conditions are described by the authors as ‘mild’, but that’s just by comparison to previous research that postulated temperatures were, back then, as high as 80°C. The authors propose that changes in clay formation processes, along with other factors, provided a ‘mitigating’ effect that was hitherto not fully appreciated.
The relevance of these findings to the modern climate system is however limited, and I would caution against it being interpreted as a viable way for the Earth to ‘heal itself’, and thus discharge us from any responsibility to mitigate the human-induced warming of the planet that is already underway. A large variety of feedback loops, both amplifiers and dampers of temperature change, are also known to exist in the present, and presumably near-future, world. Yet, Earth’s temperature is rising due to anthropogenic greenhouse gas emissions: relatively minuscule (by comparison to the changes encompassed in this study) changes of the order of 1.5-2°C compared to pre-industrial values have very large consequences for our society, as well as for other organisms. The concerns around exceeding these thresholds are exemplified by the Paris Agreement.
It would be therefore dangerous to rely on ‘natural feedback loops’ to mitigate climate change, as that would potentially lead to disastrous results for future generations.
