The sun and wind also drive the ocean’s oscillations, but it is the moon’s gravitational tug that is responsible for the lion’s share of this predictable tidal flux. Our current Earth–moon system, according to the prevailing theory of lunar formation, reflects our solar system’s early game of planetary billiards, when colliding planetary embryos created entirely new versions of themselves—in the case of our own planet, a disproportionately large natural satellite in close orbit. Without it, high and low tides would shrink by an estimated 75%. This would jeopardize the lives of many types of crabs, mussels, and sea snails that live in tidal zones and disrupt the diets of larger animals who rely on them for food, threatening entire coastal ecosystems in the process. Within a few decades, we would start to see mass population declines in the sea and on land. One of the largest spawning events in the world occurs in the Great Barrier Reef. Each November in the days following the light of a full moon, coral colonies across the reef — spanning an area larger than the state of New Mexico — release millions of egg and sperm sacs within nearly minutes of one another. Scientists are certain that the full moon plays a role in the timing, but exactly how remains a mystery. On land, animals like these Red Crabs also use lunar cues to reproduce. After living most of their lives in the mountains, millions of adult crabs migrate down to shore. And then, only during the last quarter of the moon, females release their eggs into the sea. Now, the moon may not hold as much sway over human reproduction. But without it, something else we care equally about would change — the weather. Tides and tidal currents help mix cold arctic waters with warmer waters in the tropics. This balances temperatures and stabilizes the climate worldwide. Without the moon, weather forecasts would be practically impossible. The average difference between the hottest and coldest places on Earth could grow to life-threatening extremes. The moon’s sudden absence would also confuse animals. In a 2013 review in the Journal of Animal Ecology, researchers found animals that use vision as their primary mode of interacting with the world benefit (survival-wise) from the moon’s presence. That’s no big surprise, but it does have interesting implications for the question at hand. Many predators, like owls and lions, rely on the cover of darkness with just a bit of moonlight to hunt effectively. With no moon, they would have trouble finding food. Rodents, on the other hand, tend to hide more when the moonlight is strong. It’s easier for their predators to detect them. With no moon, they would thrive. “I think you’d see some shifts in which species are common and which species are rare in a system,” says the study’s lead author Laura Prugh, a wildlife ecologist at the University of Washington. Without the Moon, the stability of Earth’s axis would be lost again, and with it, our predictable temperatures. Let us consider two cities: Rome, Italy, and Stockholm, Sweden. In summer the average high temperature in Rome is 29 °C, and in the winter the average high temperature is 13 °C. In Stockholm, the high in summer is 20 °C and in winter it is 0 °Cw1. If Earth’s tilt axis changed, the temperatures in these two cities would change dramatically. Imagine if the temperatures were swapped: the infrastructure (e.g. air conditioning or snow ploughs) would simply not be in place in those cities for humans to live, work and eat comfortably. The Italians, Swedes and all other life on Earth would need to adapt or face extinction. Furthermore, as the temperatures changed, Earth would lose its reliably cold regions: the poles, which contain huge amounts of ice. This ice would melt and the oceans would rise, changing the coastlines all around the world. Countries like the Netherlands would be covered in water. With the lack of stability in Earth’s tilt, we would also lose our regular seasons, with far-reaching consequences. Think how many organisms grow, mate, migrate or hibernate at particular times of year. And drastic changes in temperature would affect the growing season and climate for plants, making food production for the billions of people on Earth more complex.