The Vredefort Dome, Largest and Oldest Clearly-Visible Meteor Impact Structure

The Vredefort Dome is believed to be the oldest and largest clearly visible meteor impact structure in the world. It is located in South Africa, approximately 100 kilometers southwest of Johannesburg. It is approximately 250 kilometers in diameter and is thought to have formed about two billion years ago. The Vredefort Dome can be seen in the Landsat image below as a roughly circular pattern. The Vaal River can be seen meandering across the northern part of the structure.
There is evidence of at least four other impact structures on Earth that are thought to be older than the Vredefort Dome, however, these structures are no longer visible at the surface and recognizable as a meteor impact structures.

The Verdefort Dome has also been severely altered by earth processes. When first formed it was most likely a crater, however that structure has been eroded away and a ring of uplifted rocks in the area surrounding the crater are now exposed at the surface. These rocks were uplifted in a rebound action at the time of impact.

If you study the image above you will see that the northwestern part of the dome is more clearly visible than the southeastern part of the dome. This is because the southeastern part is now covered by sediments of the Karoo Supergroup.

More information about the Vredefort Dome, including photos and evidence of the meteorite impact origin has been posted by Mike Gaylard at the Hartebeesthoek Radio Astronomy Observatory website. Another website with a lot of information can be found at Vredefort Dome Geotours.