Scientists probe secrets of Earth’s climate past
Paul Cargill, PA Scotland
Mon, January 6, 2025
Researchers have shed new light on the role played by carbon dioxide in the warming and cooling of planet Earth.
A team from the University of St Andrews used fossils to work out how much CO2 changed during the Carboniferous and Permian periods between 335 to 265 million years ago, a time known as the Late Palaeozoic Ice Age.
The group found the Late Palaeozoic Ice Age had prolonged low CO2 levels until atmospheric levels rose abruptly 294 million years ago due to large-scale volcanic eruptions, warming the planet and melting the ice.
The team said their research shows how CO2 plays a pivotal role in regulating climate and environmental conditions on Earth.
Dr Hana Jurikova, the lead researcher from St Andrews, said: “The end of the Late Palaeozoic Ice Age was a turning point in the evolution of life and the environment, leading to the rise of reptiles. Now we know it was paced by carbon dioxide.”
The researchers used the chemical fingerprints stored in fossil brachiopod shells, ancient clam-like organisms which are among the oldest existing animals and still inhabit oceans today.
Such shells are preserved across all time periods of the fossil record, and provide clues to how Earth’s climate and environment has evolved.
By combining multiple chemical fingerprints, the team were able to precisely calculate how much CO2 was in Earth’s atmosphere in the past and how it changed.
Dr James Rae, who co-authored the study, added: “CO2 emissions in the past caused major global warming and sea level rise, and if left unchecked, will do so again in future.”
Their research has been published in Nature Geoscience journal.
Hana Jurikova, Senior Research Fellow, School of Earth and Environmental Sciences, University of St Andrews
Mon, January 6, 2025
THE CONVERSATION
300 million years ago, much of the planet was covered in ice. james_stone76 / shutterstock
Around 370 million years ago, Earth gradually descended into the longest lived and probably the most intense ice age witnessed by complex life: the Late Palaeozoic ice age. At its peak, huge continental ice sheets spread across much of the globe and the sea level fell by more than 100 metres. In all, this ice age lasted around 100 million years.
The transition in and out of the Late Palaeozoic ice age was one of the biggest climate transitions in Earth’s history, a turning point in the evolution of life and environment. It significantly shaped the two periods of time that made up the end of the Palaeozoic era.
First, it led to the creation of iconic “coal forests” full of giant insects in the Carboniferous period during the ice age. It also paved the way for the rise of reptiles in the Permian period that followed.
I lead an international team of scientists who have just published research demonstrating, for the first time, that carbon dioxide (CO₂) played a central role in this huge climatic transition.
The Late Palaeozoic ice age has long been a climate enigma. Atmospheric CO₂ estimates for this period vary widely, and different reconstructions of the likely temperature vary by as much as 20°C.
The occurrence of glacial deposits throughout time has often been used to track the ice age. However, this approach is biased by the incompleteness of the geological record and has only loose time constraints. When attempting to reconcile the individual pieces of the puzzle, paradoxes have emerged, such as peak ice conditions coinciding with high CO₂ levels.
Closely regulated by carbon
Our new study provides an original 80-million-year CO₂ record that tracks the climate during the descent into and emergence from the Late Palaeozoic ice age. We did this by looking at the fossilised shells of ancient clam-like creatures known as brachiopods. These shells store chemical fingerprints such as boron isotopes, which enable us to calculate how much CO₂ was in the atmosphere when the brachiopods were alive.
375 million year old brachiopod fossils. Brachiopods have been around for at least 500 million years, and their fossilised shells allow scientists to track environmental changes over the very long term. Nancy Bauer / shutterstock
This type of CO₂ reconstruction from Earth’s deep geologic past is entirely novel. Crucially, the reconstruction has a consistent timeline which enables us to bring together all pieces of the puzzle to demonstrate that the climate of the Late Palaeozoic era was closely regulated by CO₂.
What did the Late Palaeozoic climate and CO₂ look like? Our reconstruction showed that for part of this era the Earth’s atmosphere sustained relatively low CO₂ (about 330 parts per million or ppm), reaching minimum values of about 200 ppm about 298 million years ago around the boundary between the Carboniferous and Permian periods. The low atmospheric CO₂ combined with less heat coming from the younger sun would have caused the intense “icehouse” conditions, with ice sheets extending as far as the planet’s mid latitudes.
Our reconstruction also revealed an unexpected end to the icehouse period. Scientists previously thought that the Late Palaeozoic ice age gradually waned away, but our findings showed it ended much earlier. Around 294 million years ago, large-scale volcanic activity triggered a rapid rise – at least on geological timescales – in atmospheric CO₂, and Earth became warmer and drier.
While the past couple of decades have brought much progress in reconstruction of CO₂ from Earth’s more recent past (in particular the past 60 million years where we have seafloor sediments), CO₂ reconstruction from the rock record has been long considered challenging. As such, our study pushes the boundaries in geological reconstruction of atmospheric CO₂ and provides a key to unlocking its history to the beginning of Earth’s fossil record.
While CO₂ is expected to play an important role, as demonstrated during the Late Palaeozoic, precise knowledge of past levels and changes is fundamental to understanding of every aspect of the Earth system. Addressing the remaining gaps and continuously refining records is crucial to fully grasping CO₂’s influence on Earth’s climate and habitability—past, present and future.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Hana Jurikova receives funding from the Leverhulme Trust.
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