How the Earth Began
The earth was formed when the big bang occurred. It formed roughly 4.6 billion years ago when rocks circling the sun collided together. The energy made by this, created the earths core. As the planet became more circular, it started to orbit the sun. Earth was luckily able to hold life as its atmosphere lets in just enough light.
Whilst the planet developed, its plates where constantly shifting below.
They are basically laying on top of a ball of magma or the mantle. The mantle on which they lay, moves the crust above it. The crust is always changing and the face of the earth was completely different 300 million years ago.
Pangaea was the first main land mass on earth. It was a large body of land with all of the plates land mass joined. But as the continents keep on moving, Pangaea was eventually broken into the world we have today. However, Pangaea may re-form into a super continent once more. It might take around 249 MILLION years to reform, but it is still likely to happen.
The reason for Pangaea being formed and then destroyed is continental drift. Alfred Wegener suggested in 1912 that continents 'drifted' away and closer to each other. Continental drift is the movement of the Earth's continents relative to each other, thus appearing to "drift" across the ocean bed.