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Today, we have the benefit of living on a planet that is relatively comfortable, but it wasn’t always so. For much of human existence, the world was going through a rash of ice ages which reshaped the planet. The disaster movie Age of Ice (streaming now on Peacock) imagines what it might be like if a massive earthquake cracked the planet open and unleashed a modern ice age. Fortunately, there’s no reason to think that will actually happen, but a new study reveals that ice ages can come seemingly out of nowhere.

Between about 2 million and 12,000 years ago, the planet went through a series of frigid periods which blanketed the globe in snow and ice. The oceans receded as water was taken up by icebergs, glaciers, and ice sheets. Land bridges emerged and our ancestors spread across a frozen globe. The cause of those ice ages has been the subject of scientific inquiry and debate for decades, and the new study, published in the journal Nature Astronomy, offers a new and unconventional origin.

For More on the Climate:
Are Giant Arctic Viruses Combatting Climate Change?
How We’ll Avoid the Dystopian Eco-Nightmare of Mad Max
What Would the World Look Like Under a Runaway Greenhouse Effect?

The Ice Ages May Have Been Caused by Cosmic Cloud Cover

We typically think of climate and weather as relatively local phenomena, but they can be influenced by forces from not just outside of the planet, but outside of the solar system. Every 225 million years, give or take, the Sun makes an orbit around the galactic center. Meanwhile, the entire galaxy is cruising through space at 1.3 million miles per hour. The upshot is that the solar system is constantly encountering new regions of space, some of which are home to dense clouds of mostly hydrogen.

Despite being on the move through space-time, the local conditions usually stay pretty stable, because of the influence of the Sun. Charged particles from the Sun create the solar wind, which envelopes the entire solar system in a protective bubble of solar radiation known as the heliosphere. Today, that bubble extends to about 100 AU (AU stands for astronomical unit, a distance of about 93 million miles, the average distance between the Earth and the Sun). For context, Pluto’s elliptical orbit takes it from about 30 AU all the way out to over 49 AU; the heliosphere extends more than twice that distance.

The heliosphere is the dominant radiation environment in the solar system and its influence protects us from cosmic radiation coming from farther afield. But a couple of million years ago, researchers suggest, the solar system flew through a region known as the Local Ribbon of Cold Clouds (LRCC) and the heliosphere shrank to almost nothing. During this period, the heliosphere may have shriveled to a paltry 0.22 AU, roughly 20 million miles, or about halfway between the Sun and Mercury.

In short, a cold and dense cloud of hydrogen may have wiped out some of the solar system’s radiation shielding (the Earth’s magnetic field also provides some protection) and left the Earth and the rest of the planets vulnerable to cosmic radiation. Fortunately for our forebears, the impact would have been short-lived on geologic timescales. Once the solar system passed through the other side of the cloud, the Sun’s heliosphere would have taken over again, growing to envelop the system, allowing the climate to settle.

It’s a reminder that our planetary island paradise is awash in a vast cosmic sea, being battered by weather systems much larger and more powerful than we realize. Enjoy the nice weather while it’s here, there’s no telling when the forecast might change.

Age of Ice is streaming now on Peacock.