Which region was formed first?

The first region to be formed on Earth is believed to be the crust, which developed as the planet cooled and solidified after its formation around 4.5 billion years ago. This early crust was primarily composed of lighter materials that floated on the molten mantle below. Over time, tectonic processes led to the formation of more complex geological structures and regions. Thus, the Earth's crust represents the earliest stage in the development of the planet's regions.