Australian History: Gondwanaland
Millions and millions of years ago, (about 300-500 million years) it is believed that all the land on earth were joined together as one big mass of land. This one single continent was called the Pangea (which means 'all lands' in Greek) supercontinent. From Pangea, two smaller land masses began to split off, and these were Laurasia and Gondwana.
Today's continents that were a part of Gondwana include Australia, Antarctica, South America, Africa, and the regions of the Arabian Peninsula and the Indian subcontinent. which have now moved entirely into the Northern Hemisphere.
pangea animation taken from Wikipedia
How do we know that these lands were once joined?
There are many techniques that scientists use to determine this. One way is through identifying the same or similar plants/land animals that exist in different continents. These give us some proof that the continents were joined. Another method is to study rocks which when formed at any given time, freeze at a local magnetic field. The earth has a magnetic field with the North and South poles, and when rocks form as the continents drift apart, the distances from the magnetic poles can provide information.