Antarctic Plate
During the early Eocene (50 Ma), the Drake Passage between the southern tip of South America at Cape Horn and the South Shetland Islands of Antarctica was a small opening with limited circulation. A change in relative motion between the South American Plate and the Antarctic Plate would have severe effects, causing seafloor spreading and the formation of the Scotia Plate. Marine geophysical data indicates that motion between the South American Plate and the Antarctic Plate shifted from N-S to WNW-ESE accompanied by an eightfold increase in the separation rate. This shift in spreading initiated crustal thinning and by 30–34 Ma, the West Scotia Ridge formed.