Previous studies have suggested that changes in greenhouse gas levels due to volcanic activity, plate tectonics, or biological processes may have caused the Snowball Earth event. In contrast to this prevailing paradigm, the new study, published in the journal Nature Geoscience, points to variations in Earth's orbit as a primary driver.
The research team from the University of California, Davis analyzed ancient, 700-million-year-old fossils from Nevada, which provided a precise chronological framework for the changing climate prior to, during, and after the ice age. The researchers also used computer modeling to simulate the planet's orbital changes over time, allowing them to connect orbital variations and surface temperatures.
One of the study's key findings is that the Snowball Earth event did not occur gradually, as previously proposed. Instead, the researchers found evidence that the deep freeze happened more rapidly than initially thought, lasting no longer than a few tens of thousands of years. This short duration aligns well with the changes in Earth's orbit that result from its axial wobble.
The Earth's axis currently points to the North Star (Polaris), but this alignment changes slowly over tens of thousands of years. In the distant past, Earth's axis would have pointed in a different direction, and this axial wobble would have caused the angle of Earth's orbit around the sun to change periodically by up to 2.4 degrees.
These changes in the tilt and orbit slightly altered the amount of sunlight reaching Earth's poles. The reduced sunlight at the poles would have caused an initial growth of ice sheets, which would have then acted as a giant mirror and further reflected sunlight away from the planet. This positive feedback loop would have spread ice across the entire planet, leading to the Snowball Earth event.
The researchers emphasize that the axial wobble alone would not have been enough to cause such extreme cooling. It was likely accompanied by other factors, such as changes in solar output or greenhouse gas concentrations. However, they highlight that changes in Earth's orbit may have played a more significant role than previously recognized, ultimately turning our planet into a giant snowball.
Understanding the mechanisms behind extreme climate events in Earth's past can provide valuable insights for predicting and mitigating the potential consequences of future climate shifts, especially considering ongoing concerns about human-induced global warming.
