the 1950s, scientists using depth-sounding surveys discovered
an enormous undersea mountain range called the Mid-Ocean Ridge.
Measuring 42,000 miles long and up to 15,000 feet high, this
winding chain was first studied up close by Bob
Ballard in the 1970s. Exploring in the submersible Alvin,
Ballard found undersea lava formations and, later, hydrothermal
vents. His discoveries help prove that this series of undersea
volcanoes was responsible for creating the surface crust of
the entire planet.
the time of Ballard's discoveries, the body of evidence on
the Mid-Ocean Ridges and their role in the Earth's formation
had been mounting for decades.
for an illustrated tour of plate tectonics and continental