[danieltillett]

The Fermi paradox is unlikely to be answered by something making it very unlikely for our chimp level ancestors jumping to human level. The number of Homo species on the planet that co-evolved to human level intelligence suggests this is not extremely difficult.

What is a huge filter is the requirement of a stable climate over million of years. The key to this is the Moon which keeps the Earth's axis of rotation from wandering over a wide angle on geological timescales. The Moon is so large and unlikely (we still don't have a good theory for how it was formed and captured by the Earth) that this alone could explain the lack of other intelligent life in the visible universe.

[RobertoG]

>>"[..] Homo species on the planet that co-evolved to human level intelligence [..]"

Can you elaborate on this? I'm a little at lost about what you mean.

[danieltillett]

There were at least two other Homo species that co-evolved to human level intelligence separate from the one that arose in sub-Sahran Africa. The reason we know this because at least two inbred with the African Homo sapiens; Homo neanderthalensis and Homo “Desnisovan” [0].

0. https://en.wikipedia.org/wiki/Archaic_human_admixture_with_m...

[frozennorth]

Do you mind explaining why the current moon hypothesis isn't likely?

The consensus from the intro geology classes I've take seems to be that the Earth was hit by a Mars sized object which caused the resulting molten debris to coalesce and differentiate forming our current Moon in the process.

[danieltillett]

It is not that the hypothesis is unlikely [0], it is the formation of the moon that is very unlikely. When you try to simulate a collision between the Earth and Mars-sized planet it is very unlikely to create the Moon.

0. https://en.m.wikipedia.org/wiki/Origin_of_the_Moon

[wellboy]

Why is the moon so unlikely when many planets in the solar system have 1 moon or more.

[danieltillett]

The Moon is very large compared to the Earth - I have seen the Earth/Moon described as a double planet. How it formed (most likely a collision) is very, very unlikely.

All the other moons in the solar system are nowhere near large enough to stabilise the planet's axis of rotation.

[squarefoot]

The Moon also has the same rotation and revolution time, so that it always shows the same face to us. I've always wondered if having different rotation and revolution times could have helped humankind to consider the existence of spherical planets a lot before, hence helping progress.