"Our tenancy on this planet is not guaranteed."

“Early in the last century, the most powerful earthquakes ever to strike the stable heart of the continent rattled the Reelfoot Rift.”

“According to Woese's evolutionary tree, the most primary of the present-day bacteria lie within a group called the archaebacteria. All archaebacteria thrive in intense heat... Woese believes that that these modern species evolved from a similar type of ancient bacteria that... may have drawn its energy from the sulfurous compounds spewing out of hydrothermal vents. If that's true, the bacteria seen at vents today could be the closest descendents we know of the original forms of life on earth.”

“The ocean crust serves as a global water-treatment plant. Salts are removed, PH is balanced, and various minerals are added as the water continuously flushes through the crust and out the vent stacks. According to one estimate, the entire ocean passes through this filter once every ten million years.”

“In geophysical circles, the question is not so much why the sea is salty, but why it remains just as salty as it is, no more, no less.”

“Don Anderson... realized that since heat conducts only half as quickly through continental crust as through oceanic crust, the former acts like an insulating blanket. A mass as large as a supercontinent would cause the mantle to grow hotter, which would affect circulation. ...To Anderson's eye, the cluster of hotspots and the bulge in the earth exactly beneath the former site of Pangaea not only broke up the supercontinent but were formed precisely because it was preventing heat from getting out.”

“The crust and mantle churn together on both the yearly scale of incremental plate motions and the epochs of supercontinental cycling.”