Humans have pondered the question of why there is life on Earth and not anywhere else in the universe for thousands of years. In recent decades, scientific discoveries have revealed new insights into this age-old conundrum. Today, scientists are coming closer to understanding why Earth is the only planet with life. There may be many factors that make our planet unique for supporting life, but none of them are supernatural or other imaginary beings such as aliens or fairies. Therefore, we’ll look solely at natural explanations for why only Earth has life.
Why Is Earth The Only Planet With Life?
1. Earth Is Uniquely Suited For Life
The first reason why Earth is the only planet with life is that it is uniquely suited for life. The conditions on Earth that make it suitable for life are unlike anywhere else in the universe. For example, if our planet were smaller, gravity would be too weak to support life. If it were larger, gravity would be too strong to permit life. If the atmosphere were thicker, liquid water would never form on the planet. If it were thinner, all the water would evaporate. If the planet orbited too close to the Sun, the climate would be too hot for life. If it orbited too far from the Sun, it would be too cold for life. If the planet were closer to another star, it would be too hot or too cold for life. And so on.
2. Conditions On Earth Are Perfectly Calibrated For Life
Another reason why Earth is the only planet with life is that conditions on our planet are perfectly calibrated for life. We don’t know of any other place in the universe where such a delicate balance exists between life-giving and life-taking forces. As we’ve already noted, conditions on Earth are different than on any other planet.
3. Our Sun Makes A Big Difference
If our planet were closer to the Sun, the climate would be too hot for life. If it were farther away, the climate would be too cold for life. If our planet were closer to another star, it would be too hot or too cold for life. If it orbited a red dwarf star, the planet would be too warm to support liquid water. And of course, if the Sun were different, there would be no life on Earth. If the Sun were smaller, it would burn out more quickly. A larger Sun would have a lifespan thousands of times longer than the present one. So Earth has been warm enough for life for only about half of the Sun’s lifetime.
4. The Universe Is Essentially Inhospitable To Life
The Universe as a whole is essentially inhospitable to life. Most of the matter in the Universe exists in the form of cold clouds of hydrogen and helium gas. If the Universe were filled with even more matter, it would be too dense. Galaxies and stars would never have formed. If the Universe contained less matter, it would have expanded too quickly for galaxies and stars to form. There is also too little carbon, nitrogen, oxygen, iron, and other elements that are essential for life. If there were more of these elements, they would have made the Universe too dense and lacking in hydrogen and helium. If there were fewer of these elements, they would have been too rare to form the elements needed for life.
5. The Rarity Of Goldilocks Planets
Another reason why Earth is the only planet with life is the rarity of Goldilocks planets. The Goldilocks planets are the ones that are not too hot or too cold, but just right for supporting life. Earth is just the right distance from the Sun to have an environment that is not too hot and not too cold. This makes it a Goldilocks planet that is just right for life.
6. It’s Been Here For A Long Time
Another reason why Earth is the only planet with life is that it has been here for a long time. If the Earth had formed earlier, it would have been too hot for life. If it had formed later, it would have been too cold for life. If the Earth had formed earlier, stars would have been too energetic and would have shorted out before they could produce heavy elements essential for life. Later, stars would have produced too few heavy elements. If the Earth had formed later, all of the stars would have already produced heavy elements. There would have been no raw material left over to make the elements essential for life.
Why Life May Be Impossible On Other Planets?
- The biggest difference between Earth and other planets is that Earth is the only known planet with an oxygen-rich atmosphere. The presence of oxygen in our atmosphere makes life as we know it possible. Without oxygen, animals would not be able to breathe, plants would not be able to photosynthesize, and fires would not burn. The reason why oxygen is abundant on Earth and virtually absent from exoplanets has to do with the size of our planet compared to its star. Smaller planets, like Mars and Mercury, have thin atmospheres because their gravity is too weak to hold onto their gases. But even giant Jupiter has only a small amount of oxygen because it formed so far from the Sun and needed a lot of time for the elements that make up our atmosphere (like hydrogen and helium) to “rain down” onto it.
- Earth was in just the right place at just the right time for life as we know it to develop. It had just enough mass to create a protective magnetic field that shielded us from dangerous solar winds. It was also large enough that gravity could pull in gases like carbon dioxide and water vapor but not so large that it crushed all those gases into their constituent atoms or molecules — a process called “sputtering” which happens on stars with strong magnetic fields like our Sun or other hot blue stars like Rigel or Regulus.
- Earth was also just the right distance from the Sun for liquid water to flow on its surface. If it had been any closer, all of the water would have evaporated into steam; if it had been any further, all of the water would have frozen into ice. Most of the planets in our solar system are either too close or too far from their star for liquid water to exist on their surface. There are some exceptions like Jupiter’s moon Europa which has a subsurface ocean and Saturn’s moons Titan and Enceladus which have lakes of methane and ethane, respectively. But because they are so cold that they are unlikely to support life as we know it, they aren’t very interesting candidates So, life as we know it depends on three conditions:
- Oxygen: Earth is one of two planets in our solar system with an oxygen-rich atmosphere — Venus is the other one.
- Water: Earth is also one of two planets in our solar system with large bodies of liquid water — Venus is again the other one.
- Animals: The only planet in our solar system that has animals is Earth — Mars does not have animals because there isn’t enough oxygen for them to breathe; Venus does not have animals because there isn’t enough oxygen for them to breathe and there isn’t enough water for them to live on land; Mercury does not have
Earth is the only planet that is just right for life, and for that reason, it is the only planet in the entire universe with life. Our Solar System is unique with five terrestrial planets and three gas giants. The terrestrial planets are rocky planets such as Earth, Mars, Venus, and Mercury. The gas giants are Jupiter, Saturn, Uranus, and Neptune. There are millions of galaxies in the universe and billions of stars. The universe is so vast that our imagination cannot fathom it and even the most powerful telescopes cannot fully explore it because of its vastness.