system
Given the following post, respond as if you're commenting on Reddit:
human
Is Mars more like a "baby/early" Earth, or a dead Earth?

By dead Earth I mean, millions of years from now, what Earth would look like.
gpt
There are a couple differences. Earth has large amounts of liquid water. Mars has some water, but it's mostly frozen at the polar caps. Also, Mars has no magnetosphere to protect it from solar wind which caused most of its atmosphere to be stripped away. It's less than %1 as dense as our atmosphere on Earth.

There is evidence that Mars did at one time have a thicker atmosphere lots of liquid water, and a magnetosphere. For some as yet unknown reason, the liquid metallic core of mars stopped turning and this lack of a dynamo effect caused the magnetosphere to decay and mostly disappear.

If we knew what happened to Mars we'd be able say if the same fate awaits Earth. It's possible that whatever stopped the dynamo of Mars's core could also happen here. After billions of years of no magnetosphere for protection Earth could end up looking just as barren as Mars.