This is a conglomerate boulder, among the oldest rocks in the world, formed 2710 million years ago before there was life on earth. Once this area was an estuary and the pebbles were deposited at the river mouth. This part of the earth's crust was shattered and turned on its side as a result of the Vredefort meteorite strike about 2 billion years ago. These rocks are found on Johannesburg and form part of the crater impact.
The impact site was caused by an asteroid between 10 and 15 km in diameter and, had there been life on earth at the time, it would have caused a global extinction