What makes Earth so gosh darn livable? How is it different from the other planets in our solar system, or viewable planets in our galaxy?
Earth was not made to be livable. Life was made to survive on Earth.
It’s like asking why a cup is the perfect shape to hold water. The cup isn’t the key. The water is molding itself to the cup.
We have lots of things. With all of the billions of stars I’m sure life exists other places but life as we know it is limited to our situation.
We are located in a good orbit around the sun. It’s not to hot and bot to cold.
We have liquid water. Something we believe is required for life, carbon is also required.
We have a liquid core and an atmosphere. These protect us from radation.
We are a good size and density. Gravity isnt to harsh that it would crush us. It’s not so low we would float away.
Water. We have water, which is incredibly valuable to life, due to how common it is and how good it is at causing reactions.
Temperature. The temperature allows many complex molecules to form, *as well as water*.
Radiation. We’re not too irradiated, but our planet does get a fair amount of energy from the sun.
Earth has a combination of factors that made life much more likely to form here, vs anywhere else we know of.
First off, Earth’s orbit is at just the right distance from the sun to allow liquid water. Too close, and the oceans would boil. Too far, and they freeze. The region in between is called the habitable zone.
Having liquid water is important because it is a near-perfect environment for a lot of chemistry, *especially* organic chemistry.
Secondly, the sun itself is actually pretty important. It’s fairly calm as stars go, and will live quite a while. Stars that are much smaller or much bigger each have different problems.
Red and Orange Dwarfs, which are smaller than our sun, will sometimes flare violently. This can increase their brightness by as much as *eight* times! Imagine if the sun regularly became eight times brighter in the sky.
White and Blue stars, which are bigger than our sun, are much shorter lived. This likely doesn’t give any planets orbiting those stars enough time to develop complex life. Around the largest, shortest lived stars, planets won’t get enough time for *any* life, or even prebiotic chemistry.
Thirdly, Earth has a pretty strong magnetic field. This is important because, while our sun may be calm for a star, it still puts out ridiculous amounts of energy. This is mostly light, but there’s also a constant barrage of charged particles from the sun’s atmosphere. This is called solar wind, and over millions of years it will slowly blast away a planet’s atmosphere (and oceans if it has them). Fortunately, Earth’s magnetic field deflects most of the solar wind, protecting our atmosphere and oceans.
The distance from the sun, which we call the Goldilocks zone. Far enough to not get baked into barren-ness like Mercury, and close enough to not freeze up like Neptune or Uranus.
The presence of water and absence of high concentrations of more “hazardous” components, like Venus’ runaway greenhouse effect and sulfuric acid clouds.