Why Are There Two Distinct Halves on Mars?

This is called the Martian Dichotomy, and scientists are not sure what caused it, but there are three hypotheses:

1. Plate Tectonics

The Earth once had just one continent (Pangea) and one or two oceans (Panthalassa and maybe Tethys). Maybe the same thing happened on Mars?

If this was true, you would see mountain ra…