CHAPTER 1 Plate Tectonics

Earth’s Structure The Earth’s structure is made up of the following: Continental Crust Oceanic Crust The Mantle Outer core Inner Core The layers of the Earth: each layer has an effect on the geography of the surface.

The Core The core is the most centre point of the Earth. The core is made up of dense, heavy metals which sank to the centre as the Earth began to cool. The core is divided into two parts: the inner core and the outer core. A closer look at the Earth’s layers.

The Inner Core The Earth’s inner core is a solid sphere made of the metals nickel and Iron. The inner core transfers this heat to the upper layers. The transfer of heat is a vital process in making life possible on Earth. A closer look at the Earth’s layers.

The Outer Core The outer core is a 2000 km thick layer also made of nickel and iron. The outer core spins around the static inner core, causing the metals to become charged (much like a turbine used to generate electricity). The described movement generates the Earth’s magnetic field which protects us from the sun’s harmful radiation.

The Mantle The mantle is the largest layer in the Earth, making up 75 per cent of its volume. The mantle is made up of layers of rock which are molten close to the core, as it is so hot. Closer to the crust, the rock is semi-molten or solid as it is cooler. The mantle can be divided into three layers: the lower mantle, asthenosphere and lithosphere.

The Crust The crust is the outermost layer of the Earth and makes up the top part of the lithosphere. It is made of solid rock.

The Crust The continental crust is, on average, 45 km thick. The rocks which form the continental crust are light, e.g. granite. Rocks such as granite are rich in the minerals silica and aluminium – known collectively as sial.

The Crust The oceanic crust is much thinner than the continental crust. It is 8 km thick on average, but is as thin as 3 km in parts. The rocks which form oceanic crust are heavy, e.g. basalt. Rocks such as basalt are rich in the minerals silica and magnesium – known collectively as sima.

Plate Tectonics Plate tectonics states that the Earth’s lithosphere is broken into a number of slabs called plates. These plates float on top of the mantle and are constantly in motion – even if they move very slowly. The Earth’s crust is broken into sections called plates.

Plates There are seven major plates and several smaller ones. As these plates move, they collide with, separate from, or slide past each other along their boundaries. It is along these plate boundaries that nearly all earthquakes, fold mountains and volcanoes occur. Plate tectonics explains how and why this movement occurs.

Continental Drift German meteorologist, Alfred Wegner, developed the theory of continental drift. The theory of Continental Drift states that the world’s continents are constantly moving.

Continental Drift According to Wegner, all landmasses were originally joined together in one super continent he called Pangaea. Pangaea

Continental Drift Wegner suggested that Pangaea first broke into two smaller supercontinents he named Gondwanaland and Laurasia, before eventually forming the continents and oceans we see today. Continental Fit, Matching Fossils and Matching Folds are frequently cited as proof of Continental Drift. Matching fossils of plants and animals

Convection currents Arthur Holmes theorised on the movement of plates. The theory states that Magma heated in lower mantle, rises towards lithosphere, cools and becomes semi-molten, moves sideways and sinks, sideways movement causes friction. This friction results in the movement of plates.

Mid-Ocean Ridges Maurice Ewing discovered a chain of underwater volcanoes and mountains along the middle of the Atlantic Ocean. This chain became known as the Mid-Atlantic Ridge. Ewing also discovered that the ocean floor was made of basalt and was much thinner than usual close to the ridge. This suggested that plates were pulling apart at this point.

Seafloor Spreading New seafloor is made at mid-ocean ridges. As new seafloor is created, older seafloor is pushed towards continents making the oceans wider. The age of seafloor and ocean sediments are cited as proof of Seafloor Spreading.

Subduction When an oceanic plate collides with a continental plate, the oceanic plate’s heavier weight means it sinks back down into the mantle. It melts back into magma by the extreme heat. When two oceanic plates collide, the heavier plate sinks underneath the lighter one. This process is called subduction. This means that the Earth is constantly recycling its lithosphere. Subduction Zone