The Earth's climate is a complex and dynamic system, and it turns out that the movement of our planet's surface plays a more significant role in climate change than we ever imagined.
Our planet has gone through incredible climate transformations, swinging between frigid icehouse periods and warm, almost tropical greenhouse states. Scientists have traditionally linked these shifts to carbon dioxide levels in the atmosphere, but recent research reveals a much more intricate story.
Here's where it gets controversial: The source of this carbon and the forces driving climate change are far more complex than previously thought. It's not just about atmospheric carbon; it's about the intricate dance between carbon emissions from Earth's surface and how they're trapped in sediments on the ocean floor.
The way tectonic plates move and interact with each other has a major impact on climate, and it's an aspect that has been underappreciated until now. Carbon isn't just released where plates collide; the places where they pull apart are just as significant.
Our new study, published in Communications, Earth and Environment, sheds light on how Earth's plate tectonics have shaped global climate over the past 540 million years. By peering deep into the carbon cycle, we've uncovered some fascinating insights.
At the boundaries where tectonic plates converge, we find volcanic arcs, chains of volcanoes that unlock carbon trapped in rocks for thousands of years, bringing it to the Earth's surface. Historically, these volcanic arcs were thought to be the primary culprits for injecting carbon dioxide into the atmosphere.
But our findings challenge this view. We suggest that mid-ocean ridges and continental rifts, where plates spread apart, have played a much more significant role in driving Earth's carbon cycles throughout geological time. This is because the world's oceans act as vast carbon sinks, storing most of the atmospheric carbon dioxide in carbon-rich rocks on the seafloor. Over thousands of years, this process can create hundreds of meters of carbon-rich sediment at the bottom of the ocean.
As these carbon-rich rocks move with the tectonic plates, they may eventually reach subduction zones, where plates converge. Here, they release their carbon dioxide cargo back into the atmosphere, completing the deep carbon cycle. To track this process, we use computer models that simulate the migration of tectonic plates through geological time.
Our study reveals that during greenhouse periods, when Earth was warmer, more carbon was released than trapped in carbon-carrying rocks. In contrast, during icehouse climates, carbon sequestration in the oceans dominated, lowering atmospheric carbon dioxide levels and triggering cooling.
One of the key takeaways is the critical role of deep-sea sediments in regulating atmospheric carbon dioxide. As tectonic plates move, they carry carbon-rich sediments, which are eventually returned to Earth's interior through subduction. This process is a major factor in determining whether Earth is in a greenhouse or icehouse state.
The carbon emitted from volcanic arcs has historically been considered one of the largest sources of atmospheric carbon dioxide. However, this process only became dominant in the last 120 million years, thanks to planktic calcifiers, tiny ocean organisms that excel at converting dissolved carbon into calcite. These creatures are responsible for sequestering vast amounts of atmospheric carbon into carbon-rich sediment on the seafloor.
Before the evolution and spread of planktic calcifiers, carbon emissions from mid-ocean ridges and continental rifts contributed more significantly to atmospheric carbon dioxide levels. So, the high proportion of carbon emitted along volcanic arcs in the past 120 million years is largely due to the carbon-rich sediments created by these organisms.
Our findings offer a new perspective on how Earth's tectonic processes have shaped, and will continue to shape, our climate. It's not just about atmospheric carbon; it's about the delicate balance between emissions from Earth's surface and the carbon trapped in seafloor sediments.
This study provides crucial insights for future climate models, especially in the context of rising carbon dioxide levels and the ongoing effects of human activity. We now understand that Earth's natural carbon cycle, influenced by the shifting tectonic plates beneath our feet, is a vital regulator of the planet's climate.
By embracing this deep time perspective, we can better predict future climate scenarios and the impact of our actions on the planet. So, the next time you feel the Earth move beneath your feet, remember, it's not just about the ground shaking; it's about the intricate dance of carbon that shapes our climate.
