A new study suggests that Mars, a "neighbor" tens of millions of kilometers away, may have played a key role in the history of Earth's repeated glacial periods. Stephen Kane, an astronomer at the University of California, Riverside (UC Riverside), used computer simulations to find that Mars' gravitational disturbances will change the Earth's orbit on extremely long time scales, thereby amplifying the dramatic climate swings between glacial and interglacial periods.
In public opinion, "climate" and "weather" are often used interchangeably, but the two are distinct in time scales and complexity. Weather changes are measured in hours, days, weeks, and even months, while climate is a long-term system spanning decades, centuries, and even millions of years, superimposed on multiple, interacting cyclical changes. From the familiar El Niño and La Niña to decadal oscillations lasting 10–80 years, these are just “short cycles” in the climate system, and are still “minuscule” compared with the ultra-long cycles that truly dominate geological history.
Among these ultra-long cycles, the more familiar to the scientific community are the orbital cycles formed by the combined action of Venus and Jupiter, known as part of the Milankovitch cycle. These include the roughly 405,000-year "Metronome" and "Modifier" cycles, which cause the Earth's distance from the Sun to change significantly over the course of a year by pulling the Earth's orbit from a near circle to a slightly elliptical one. This causes the amount of solar radiation the Earth receives to fluctuate by up to about 23% over long timescales, providing a "background rhythm" for the formation of ice ages.
Kane's latest simulation shows that Mars is not an insignificant supporting role in this system, but a secret and critical "mixer." He originally thought that Mars was less massive and far away, and that its gravity would have a negligible impact on the Earth's climate, but numerical results overturned this assumption. The study points out that if Mars were "removed" from the solar system, the Earth's pattern of frequent and violent switching between deep glacial periods and warm interglacial periods over the past approximately 2.6 million years would no longer exist.
According to the current mainstream theory, Venus and Jupiter provide a long-term "beat" for the Earth's orbit, which determines the overall magnitude of changes in the scale of glaciers, but does not directly create ice ages. Mars' gravity adds to this a "grand cycle" of about 2.4 million years, which can be traced in the geological record through hiatus in deep-sea sediments. These discontinuities occur when deep-ocean currents become so strong at certain stages that they erode the seafloor, making it difficult for sediment to accumulate, leaving "gaps" in the seafloor strata.
The function of this grand cycle is to make the glacial period more "cold" and the warm period "warmer", while intensifying the magnitude and speed of the transition between the two. The long-term gravitational disturbance of Mars changes the Earth's orbital parameters, causing the solar radiation distribution pattern to be continuously fine-tuned on extremely long time scales, triggering or amplifying key threshold processes for glacier expansion and retreat. This also means that the seemingly violent climate jumps that the Earth has experienced in the past few million years are likely to have deep connections with the red planet.
The significance of this discovery has gone beyond planetary dynamics itself and has begun to affect discussions on the origin and evolution of human beings. Some anthropologists believe that rapid climate shifts caused by orbital cycles prompted the transition from forests to grasslands in large areas of Africa, reshaping the environment that ancient humans relied on for survival. Under pressure from forests to retreat and open grasslands to expand, early humans were forced to adapt to new ecological niches, leading to bipedal walking and the development of larger brains.
For modern humans, Mars' long-term "control" of the Earth's climate also reminds people that the climate warming currently discussed is superimposed on a complex orbit and climate background that is pulled by multiple planets for a long time. Although climate change driven by human activities occurs on extremely short time scales, its effects are ultimately reshaped and amplified or attenuated during these natural cycles that span hundreds of thousands or even millions of years. In this grand picture of the universe, Mars is no longer just an imaginary target for future human immigration, but also a silent but critical "pushman" behind the history of Earth's climate.