The section shows a mid-ocean ridge with a rift valley along its crest and lava erupting into that valley. Where is the youngest crust?

The section shows plates moving away from a ridge crest in opposite directions, with arrows pointing outward on both sides. What does this pattern show?

In the cross section, point A marks a narrow valley at the ridge's crest where lava erupts. What is happening at point A?

Two seafloor rock samples are collected at a ridge like the one shown, each the same distance from the crest but on opposite sides. Which sample has older crust?

The section shows a rift valley with steep walls at the ridge crest, flanked by older crust farther out on both sides. What does the widening gap between the plates represent?

The section shows arrows pointing outward from the ridge on both plates, matching mantle material rising beneath the ridge. What drives this plate motion?

The figure shows magnetic stripes on the seafloor of the same widths and in the same order on both sides of a ridge. What does the symmetry show?

The figure shows alternating light and dark magnetic stripes running parallel to a mid-ocean ridge. What do the alternating stripes record?

Suppose one magnetic stripe beside a ridge like this one is noticeably wider than the stripes next to it on the same side, and the spreading rate has stayed constant. What does the wider stripe indicate?

The figure shows a mirror-image stripe pattern on either side of the ridge crest. What does this symmetry provide evidence for?

A ship towing a magnetometer records the strength of magnetism in seafloor rock while crossing a mid-ocean ridge. What pattern does it detect?

Two ridges show magnetic stripes of the same age. Ridge X's stripes are wider than Ridge Y's. What does this suggest?

The table shows sediment thickness at two seafloor locations. What does this pattern show?

The table lists seafloor age at increasing distances from a ridge crest. Based on the pattern, what is the relationship between distance from the ridge and crustal age?

The table lists the distance and age of four seafloor rock samples from a ridge crest. Which sample has the oldest crust?

Use the table of sediment thickness and distance from a ridge crest. What causes the farther site to have thicker sediment?

The table lists the age and sediment thickness of seafloor at several distances from a ridge crest. What does the relationship between age and sediment thickness confirm?

At a ridge crest, sediment thickness is nearly zero, but 300 kilometers away it is over 500 meters. What does the near-zero thickness at the crest indicate?

Harry Hess reasoned that if new seafloor is made at ridges, older seafloor must be destroyed somewhere. Where did he say it goes?

Harry Hess proposed that the ocean floor forms at mid-ocean ridges and is destroyed at trenches. What is this hypothesis called?

Hess supported seafloor spreading partly with measurements of which seafloor property, which is thinnest near ridges and thickest near continents?

Which scientist proposed that the seafloor spreads apart at mid-ocean ridges and sinks back into the mantle at trenches?

Rock 60 kilometers from a ridge crest formed 3 million years ago. What is the average spreading rate on that side of the ridge?

Rock 45 kilometers from the Mid-Atlantic Ridge formed 3 million years ago. What is the average spreading rate?

The East Pacific Rise spreads at about 15 centimeters per year. About how far from the ridge crest is crust that formed 2 million years ago?