John Maddox looks at new research which sheds light on the differences between Earth and the other planetsby John Maddox / November 20, 1996 / Leave a comment
Published in November 1996 issue of Prospect Magazine
Why is the Earth so different from Venus, and for that matter from Mars and Mercury? Venus, as massive as the Earth, has a thick atmosphere of carbon dioxide, which keeps the surface of the planet well above the boiling point of water. Mars, smaller than the Earth and further from the Sun, has a tenuous atmosphere of carbon dioxide. Mercury, the innermost planet, is simply bare rock. How did the inner planets of the solar system acquire these features?
The truth is that nobody knows for sure. At some level, the explanation must involve accidents going back to the start of the solar system-between the formation of the Sun 5,000m years ago and that of the Earth 4,500m years ago.
Now the Earth’s history has been put in a clearer light by two people from Harvard-Charles Harper and Stein Jacobsen. Writing in Science, they use geological evidence to show that the formation of the Earth took no more than 100,000 years after the Sun itself had formed.
How can geological evidence throw light on questions such as the composition of the Earth’s early atmosphere? It’s not the conundrum it may seem, for the Earth should contain traces of the gases from the Earth’s early atmosphere. So much has been recognised for years. The new development is that Harper and Jacobsen have been able to make sense of previously conflicting data.