NASA

The Apollo 17 crew took this image of Earth on Dec. 7, 1972 while headed to the Moon. It was the first time an Apollo trajectory allowed a photograph of the Antarctic ice sheet, seen here at the bottom of the globe.

December is summer time at the South Pole, which is why it's all illuminated by the Sun. The African continent dominates the image, with Madagascar sitting off the coast, just about at the center of the photo.

The obvious chunk taken out of the top-right of the continent is the Middle East, dominated by Saudi Arabia (in terms of total land area) with the Red Sea parting the two land masses. The ongoing action illustrates how Earth's crust is divided into about a dozen major plates that move constantly. The Middle Eastern land mass was, in fact, torn from Africa long ago as two plates spread apart.

The spreading continues, and scientists speculate that three plates meeting at the edge of the present-day African continent will separate. If that happens, the Indian Ocean will flood the area, making the easternmost corner of the continent, known as the Horn of Africa, a large island.

-- Robert Roy Britt