Scientists have made very precise measurements of the positions of the plates and shown that they are moving relative to each other at typical speeds of less than an inch (a few cm) per year. The North & South American plates are measured to be separating from the European and African plates at a net speed of 2 cm per year. The Atlantic Ocean is about 5,000 km (500,000,000 cm) wide. Assuming that the speed of plate tectonics has been approximately constant, how long ago would you estimate that North & South America split off from Europe & Africa