Core Dive

Core Dive: the structure of the Earth for Cambridge IGCSE Marine Science

This free game is part of our Cambridge iGCSE Marine Science (0697) course for exams in EXAM YEARS 2027-2029.

The layers of the Earth

In Core Dive you pilot a drilling pod from the floor of the Pacific Ocean, 4 km below the waves, all the way to the centre of the Earth, 6,371 km down. It covers the Earth's structure in the Cambridge IGCSE Marine Science (0697) course.

• Crust: the thin, rocky outer skin. Under the oceans it is made of a dark volcanic rock called basalt. No real drill has got further than about 12 km.
• Mantle: the thickest layer, reaching down to about 2,900 km. Magma comes from here, but most of the mantle is solid rock that flows very slowly in convection currents: hot rock rises, cools and sinks, like soup in a pan.
• Outer core: from about 2,900 km. It is made of metal, mainly iron, so hot that it has melted - about as hot as the surface of the Sun.
• Inner core: from about 5,150 km. It is even hotter, yet solid, because of the enormous pressure. It is a ball of iron about 1,220 km in radius, smaller than the Moon (1,737 km).

How earthquake waves prove the outer core is liquid

Nobody has been to the core, so how do we know what it is like? Earthquake waves:

• P-waves are push-pull waves. They travel through solids and liquids, and arrive first.
• S-waves are side-to-side shaking waves. They can only travel through solids.

S-waves stop dead at the outer core, which shows it is liquid and creates an S-wave shadow zone on the far side of the Earth. P-waves slow down and bend (refract) when they enter the liquid core, giving a P-wave shadow zone between about 104° and 140° from the earthquake. In 1936 the Danish seismologist Inge Lehmann noticed faint P-waves inside the shadow zone and showed they had bounced off a solid inner core.

The magnetic field, plates and the sea floor

Liquid iron swirling in the outer core works like a giant dynamo and makes the Earth's magnetic field. It steers most of the solar wind away from Earth, making auroras at the poles, and some animals, such as loggerhead turtle hatchlings, use it like a built-in compass to cross the ocean.

The crust is broken into tectonic plates carried by mantle convection. At the Mid-Atlantic Ridge two plates move apart by about 2.5 cm a year, and magma rises to form new sea floor. As it cools, iron-rich minerals line up with the magnetic field. The field has flipped many times, so the rocks form matching magnetic stripes on each side of the ridge. Near the ridge, hydrothermal vents pour out super-hot, mineral-rich water, where bacteria use chemicals instead of sunlight to make food.