On today's Alley Oop - 4 November 2020

 So the nonsense trend continues. I'm guessing 4 billion years ago would likely be when the Earth was struck by some object. Some quick research found this:

Water arrived on Earth at exactly the same time that the moon was created over 4 billion years ago, according to a new study. This phenomenon is thought to have happened when an “ancient planet” called Theia smashed into Earth

It will be interesting (highly unlikely however) to see what our aspiring "adventure" writer does with this scenario. As usual, we get another silly "joke" by Oaf in the last panel. With any luck, our hapless trio will arrive seconds before the planet smashes into the Earth. Unfortunately it will likely be some lame event where Oaf goes looking for an arcade like the last time travel fiasco.