The Hadean geologic eon began when the Earth was formed an estimated 4.6 billion years ago and ended approximately 800 million years later. There remain few geological traces of this period on Earth, but toward the end of the 20th c, geologists identified a few rocks and zircon crystals that dated to the Hadean. The eon's name is derived from Hades, a Greek word now used as a synonym for hell, and may be a reference to the conditions on Earth at the time. How hot was Earth's surface then?
Back in the day
German mathematician, astronomer, and astrologer Johannes Kepler was a key figure in the 17th century astronomical revolution. He formulated the three laws of planetary motion and laid the foundation for the study of celestial mechanics. Kepler stated that the shape of each planet's orbit is an ellipse with the sun at one focus and that the speed of a planet depends on its distance from the sun. The third law establishes a relationship between a planet's average distance from the sun and what?
Born on a day like today
The multitalented Tapio Rautavaara of Finland was a successful athlete, singer, and actor. He won a gold medal in the javelin throw event at the 1948 Summer Olympics and was also a top archer. He acted in numerous Finnish films and recorded a total of 310 songs before his death in 1979. Rautavaara suffered a brain injury during a slip-and-fall accident, but medical officials failed to identify the symptoms of a fatal cerebral hemorrhage and sent him home. What did they think was wrong with him?