"How long has the moon
And earth been together like this?"—
Earth formed 4.6 billion years ago and then a Mars-sized object hit 100 million years later. It was from the Saturn-ring like wreckage that our Moon formed. Here's how big it used to look in our sky thereafter #BTSArmy

The Moon currently moves away from us at a rate of 3.8cm/year. But this 'lunar retreat' rate has varied from 0.13 – 28 cm/year over the last 4.5 billion years

Tidal forces cause the Moon to retreat, so let's talk about that

The Moon lifts our oceans (+ some Earth) towards it, but Earth rotates these oceans away from the Moon. The oceans still pull the moon tho, making it orbit Earth faster. The key: a faster orbit means it better-escapes Earth's gravity, so it has a larger orbit as a result!

The 'lunar retreat' has varied 0.13 – 28 cm/year over the last 4.5 billion years, here's how:
1) asteroids impacting Earth or Moon
2) movement of Earth's landmasses (via earthquakes)
These changes have affected how Earth pulls on the Moon over time

Data/info here is from a great science paper by de Azarevich et al., (2017) https://doi.org/10.1007/s00367-017-0500-z & references therein

Earth would have spilled its interior into space during the collision, so part of the Moon is ancient Earth, and part of the Earth is ancient Moon... things were pretty explosive back then, like #Dynamite