What was the first continent on Earth?

Hint: A continent is a big landmass that is made up of multiple smaller land masses. Up to seven regions are typically regarded as continents and are generally recognised by convention rather than any rigorous criteria. Asia, Africa, North America, South America, Antarctica, Europe, and Australia are the seven regions, in order of area, from largest to smallest.

Complete answer:
Earth didn't have seven continents 300 million years ago; instead, it had one gigantic supercontinent called Pangaea, which was encircled by a single ocean named Panthalassa.

During the late Paleozoic and early Mesozoic periods, Pangaea existed. It formed around 335 million years ago from older continental units and began to disintegrate around 175 million years ago. Pangaea was centred on the Equator and encircled by the superocean Panthalassa, in contrast to the current Earth and its dispersal of continental mass. Pangaea is the newest supercontinent to exist, as well as the first to be recreated by geologists.

The existence of Pangaea was first suggested by the geography of the continents bordering the Atlantic Ocean. The seeming closeness of the North and South American coastlines to those of Europe and Africa was noted almost as soon as these coasts were surveyed. Abraham Ortelius, who lived in 1596, may have been the first to claim that these continents were previously connected and then split.

Note: Pangaea is the newest supercontinent to be discovered in the geologic record. Supercontinent formation and disintegration seems to have occurred in a cyclical pattern throughout Earth's history. Before Pangaea, there could have been a few more.