Science 

Junior Science Corner

Episode 1

Welcome to Junior Science Corner! This newsletter segment contains student work from the Koonung Year 7, 8 and 9 Science program. We hope you enjoy it.

Is the seafloor really spreading? When I go to the beach, it doesn’t look like it!

Several types of evidence support the theory of sea-floor spreading: sea floor drills, magnetic stripes (within the rock of the ocean floor), and the ages of the rocks themselves.

Figure  SEQ Figure \* ARABIC 1 - Mid-oceanic ridges appear where tectonic plates are moving apart, due to the upthrust of magma to fill the gap between plates

The first proof of sea-floor spreading came from rock samples obtained by drilling into the ocean floor. The Glomar Challenger, a drilling ship built in 1968, gathered the samples. The Glomar Challenger sent drilling pipes through water six kilometres deep to drill holes in the ocean floor. Samples from the sea floor were brought up through the pipes and the scientists then determined the age of the rocks from studying the samples. They found that the farther away from a ridge the samples were taken, the older the rocks were. The youngest rocks were always in the centre of the ridges.

When scientists studied patterns in the rocks of the ocean floor, they found more support for sea-floor spreading. It was discovered that the rock that makes up the ocean floor lies in a pattern of magnetized ‘stripes’. They found that stripes of rock that formed when Earth’s magnetic field pointed north alternate with stripes of rock that formed when the magnetic field pointed south. Magnetic stripes in the rock of the ocean floor show the direction of Earth’s magnetic field at the time the rock hardened.

It was also found that the older rocks were denser and thicker compared to the thinner and less dense rocks in the mid-oceanic ridge. This means that the magma that leaks from the ridge pushes the old rocks away and as they increasingly become distant, they become older, denser, and thicker. On the other hand, the newest, thinnest crust is located near the centre of the mid-ocean ridge, the actual site of seafloor spreading.

The seafloor really is spreading, even though it doesn’t look like it at the beach!

Written by Zac Macfarlane, 9G; diagram by Joelle Hong, 9D.