Cambridge IGCSE Marine Science 1: The Earth and its oceans

Cambridge 0697 begins by placing the oceans within a dynamic Earth system. Topic 1 covers Earth structure, plate tectonics, the location and form of oceans and seas, and the causes and consequences of tides and currents. The separate practical hub owns detailed measurement methods; this theory chapter explains what the measurements represent.

Earth, Moon and internal structure

Earth is a planet orbiting the Sun, while the Moon is Earth's natural satellite. Gravity supplies the inward force that keeps Earth in its orbit around the Sun and the Moon in its orbit around Earth.

The syllabus uses a three-part Earth model. The core is iron, with a solid inner core and liquid outer core. Movement associated with the iron core creates Earth's magnetic field. The mantle is solid rock that can melt to form viscous magma. The crust is the outer layer of solid rock. Keep these material and state descriptions distinct: the mantle is not simply a global liquid ocean of magma.

Plate tectonics and ocean basins

The crust is divided into tectonic plates. In the syllabus model, plates float on the mantle and move through convection currents. Over hundreds of millions of years, supercontinents broke apart and plates moved, producing the present arrangement of continents and oceans.

At a divergent boundary, plates move apart. Magma can rise and solidify, forming new crust and features such as mid-ocean ridges. At a convergent boundary, plates move together. One plate may descend, and earthquakes and volcanoes can occur. At a transform boundary, plates move past one another; accumulated stress can be released as earthquakes.

A tsunami may form when sudden displacement of the seabed moves a large water mass, commonly after an undersea earthquake. In deep water the wave can travel rapidly with modest height. As it reaches shallower coastal water, it slows, shortens and grows higher. Impacts can include habitat damage, sediment redistribution, salt-water intrusion, organism mortality, loss of buildings and infrastructure, injury and displacement. A tsunami is not an ordinary tide and is not caused by the daily tidal cycle.

The World Ocean

The five named oceans are Arctic, Atlantic, Pacific, Indian and Southern. They are interconnected and encircle Earth as one World Ocean. Oceans cover about 71 percent of Earth's surface and contain about 97 percent of its water. The Pacific is the largest ocean. The Mariana Trench reaches approximately $11,000\text{ m}$