Why the map looks like this

Plates in slow motion.

Plate tectonics

The crust is broken into plates moving a few centimetres a year. Where they collide, mountains rise; where they pull apart, oceans open; where they slide past, earthquakes concentrate.

The Himalayas are still rising as India pushes into Asia.
The Pacific Ring of Fire follows subduction zones around that ocean.

Reading the evidence

Matching coastlines, shared fossils and magnetic stripes on the sea floor all record continents that were once joined and have since drifted apart.