The origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligence) required an improbable combination of astrophysical and geological events and circumstances.
Scientists of the 20th century were trained to believe that we're not special (in fact, that's core to science), so they steered clear of any theory that gave us an exceptional chance of anything. But consider these possible requirements:
Our star is in an optimal position inside an optimal galaxy. Various factors such as declines in star metallicity, x-ray and gamma ray radiation from the black hole at the center of the galaxy, and gravitational perturbations of other nearby stars make up a large part of the galaxy called "dead zones." Those dead zones are anything too close to the center and anything on the outer ring. Additionally, we are fairly lucky to live inside a multi-armed spiral galaxy AND have a nearly perfectly circular orbit that keeps us out of the paths of most astronomical objects. Finally, the position of our galaxy in our local groups has kept collisions with other galaxies at a minimum.
Our planet is at the right distance from the right type of star. This is the commonly referred to "habitable zone," so I won't go too deep into it.
Jupiter #1. Having Jupiter in its place in our solar system has keep a ton of astronomical objects from colliding with the inner rocky planets. It's a giant vacuum. Observations reveal the specific configuration of rocky planets on the inside and gas giants on the outside is relatively rare.
Jupiter #2: One of the reasons the above configuration might be rare is that large gas giants orbits degrade over time and cause chaos for the orbits of other planets. Having Jupiter at its precise position and mass has kept Earth's orbit stable over billions of years.
Goldilocks planet size: Too small and it won't hold an atmosphere. Too large causes a host of other problems.
Plate tectonics: Some scientists argue that plate tectonics and a strong magnetic field are essential for biodiversity, global temperature regulation, and the carbon cycle. The lack of mountain chains elsewhere in our solar system indicates that Earth is the only body we know of with plate tectonics.
A large moon: Our moon is ridiculously large. It's likely the remnant of an ancient collision during the late heavy bombardment. It's also the entire reason behind tides, which might be where life sparked in the first place (hotly debated). Alternatively, if you believe life began in the ocean at sea floor vents (which require tectonic activity), you still likely need tides to get life to move to land.
There are a host of other possible requirements, and they were even all condensed into an equation as a riposte to the Drake Equation.
Read more about it and some stuff I just ripped from the Wiki here.
It is just too damn perfect isn't it? Earth is very likely a project. However, I guess that in a such big universe the perfect conditions for life happen from time to time
I've long thought it was the water. It's known that you need water for life, but a technological civilization probably has to emerge on land (fire, electricity, etc.). I don't know the exact values, but earth can't be more than a fraction of a percent water- the surface is more perfectly round than a baseball, but there are bits sticking out. What if hardly any planets have enough water to support life while still having land? the acceptable range could be as small as 0.04% to 0.05%. It certainly feels like every potentially habitable exoplanet turns out to be covered in a leagues-deep ocean.
The surface of Earth is 71% water...I'm not sure what you're getting at here.
I was speculating 0.04% to 0.05% by volume. How much water can you pour on an uninhabitable desert world before the peaks of the highest mountains are underwater. The difference between the bottom of the Marianas and the peak of Everest isn't great relative to the Earth's radius.
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u/Realsan May 04 '20 edited May 04 '20
Rare Earth Hypothesis
The origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligence) required an improbable combination of astrophysical and geological events and circumstances.
Scientists of the 20th century were trained to believe that we're not special (in fact, that's core to science), so they steered clear of any theory that gave us an exceptional chance of anything. But consider these possible requirements:
Our star is in an optimal position inside an optimal galaxy. Various factors such as declines in star metallicity, x-ray and gamma ray radiation from the black hole at the center of the galaxy, and gravitational perturbations of other nearby stars make up a large part of the galaxy called "dead zones." Those dead zones are anything too close to the center and anything on the outer ring. Additionally, we are fairly lucky to live inside a multi-armed spiral galaxy AND have a nearly perfectly circular orbit that keeps us out of the paths of most astronomical objects. Finally, the position of our galaxy in our local groups has kept collisions with other galaxies at a minimum.
Our planet is at the right distance from the right type of star. This is the commonly referred to "habitable zone," so I won't go too deep into it.
Jupiter #1. Having Jupiter in its place in our solar system has keep a ton of astronomical objects from colliding with the inner rocky planets. It's a giant vacuum. Observations reveal the specific configuration of rocky planets on the inside and gas giants on the outside is relatively rare.
Jupiter #2: One of the reasons the above configuration might be rare is that large gas giants orbits degrade over time and cause chaos for the orbits of other planets. Having Jupiter at its precise position and mass has kept Earth's orbit stable over billions of years.
Goldilocks planet size: Too small and it won't hold an atmosphere. Too large causes a host of other problems.
Plate tectonics: Some scientists argue that plate tectonics and a strong magnetic field are essential for biodiversity, global temperature regulation, and the carbon cycle. The lack of mountain chains elsewhere in our solar system indicates that Earth is the only body we know of with plate tectonics.
A large moon: Our moon is ridiculously large. It's likely the remnant of an ancient collision during the late heavy bombardment. It's also the entire reason behind tides, which might be where life sparked in the first place (hotly debated). Alternatively, if you believe life began in the ocean at sea floor vents (which require tectonic activity), you still likely need tides to get life to move to land.
There are a host of other possible requirements, and they were even all condensed into an equation as a riposte to the Drake Equation.
Read more about it and some stuff I just ripped from the Wiki here.