The 2.25 billion-year-old Yarrabubba crater in Western Australia has recently been identified as the world's oldest impact crater. It is said to be 43 miles (69 km) in diameter, yet the photo which accompanies the news item shows a circular structure about 430 metres across, hardly more than quarter of a mile. I realise there has been massive erosion since the crater was formed, but erosion to this extent is hard to believe.
The Manicouagan crater in Quebec has a clearly visible diameter of 62 miles (100 km). which is its official diameter. Its age is 214 million years. Erosion to the same extent as is claimed for the Yarrabbuba crater would give Manicouagan an original diameter of about 10,000 miles (16,000 km)! Clearly this is impossible, so being only about a tenth the age of the Australian example it has eroded far less. But that is not the same as no erosion at all.
Can anyone give an approximate diameter of Manicouagan at the time it was formed? Another peculiarity of the Yarrabbuba crater is that in the photo it appears to be slightly domed rather than sunken. Is this an artefact of the photograph, a sort of optical illusion, or is it really raised?