Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: Main Tectonic Plates and Movement
Our planet is made up of several distinct layers, each with different properties. Understanding these layers helps explain why tectonic plates move and interact the way they do.
Key Definitions:
The Earth's crust varies in thickness - oceanic crust (5-10km) is thinner but denser than continental crust (30-70km). The mantle makes up about 84% of Earth's volume and contains semi-molten rock called magma. The core reaches temperatures of up to 5,500°C, with the inner core remaining solid despite extreme heat due to immense pressure.
When Earth formed about 4.6 billion years ago, heavier materials sank towards the centre while lighter materials rose to the surface. This process, called differentiation, created the layered structure we have today. The heat in the core drives convection currents in the mantle, which power plate movements.
The Earth's lithosphere is broken into large pieces called tectonic plates that float on the semi-molten asthenosphere below. These plates move very slowly - typically just a few centimetres per year.
There are seven major plates and numerous smaller ones. The major plates include:
The largest plate, mostly oceanic, moving northwest at 7-11cm/year.
Covers Europe and most of Asia, moving eastward at about 2cm/year.
Includes North America and part of the Atlantic Ocean, moving westward at about 2.3cm/year.
Other major plates include the African, South American, Indo-Australian and Antarctic plates. There are also many smaller plates such as the Nazca, Philippine and Caribbean plates.
Where tectonic plates meet, we find different types of boundaries. Each type creates distinctive landforms and geological activity.
Where plates move towards each other. This can create mountains (continental-continental collision), trenches and volcanoes (oceanic-continental collision), or deep trenches (oceanic-oceanic collision).
Where plates move away from each other, creating rift valleys on land or mid-ocean ridges underwater. New crust forms as magma rises to fill the gap.
Where plates slide past each other horizontally. These don't create or destroy crust but cause earthquakes as plates snag and release.
Tectonic plates don't move by themselves - they're driven by powerful forces within the Earth.
Heat from the core causes material in the mantle to rise, cool and sink in a circular motion. These convection currents drag the plates above them, similar to how a conveyor belt works. Hot material rises at divergent boundaries and cooler material sinks at convergent boundaries.
Ridge push: The elevated position of mid-ocean ridges allows gravity to push plates away from the ridge.
Slab pull: When oceanic crust subducts, it pulls the rest of the plate with it. This is considered the strongest force driving plate movement.
Different types of convergent boundaries create different landforms:
Forms volcanic mountain ranges like the Andes. The denser oceanic plate subducts beneath the continental plate, creating a deep ocean trench and volcanic arc.
Creates fold mountains like the Himalayas. Neither plate subducts; instead, they crumple upwards as they collide.
Forms island arcs like Japan. One oceanic plate subducts beneath another, creating a deep trench and a chain of volcanic islands.
When plates move apart, they create distinctive features:
Forms rift valleys like the East African Rift. The crust stretches and thins, creating a long, deep valley with steep sides. Eventually, this can split a continent and form a new ocean.
Creates mid-ocean ridges like the Mid-Atlantic Ridge. Magma rises to fill the gap between plates, creating new seafloor in a process called seafloor spreading.
The Pacific Ring of Fire is a horseshoe-shaped belt around the Pacific Ocean where about 75% of the world's volcanoes and 90% of Earth's earthquakes occur. This concentration of tectonic activity happens because the Pacific Plate is surrounded by convergent boundaries where it subducts beneath surrounding plates. Major volcanoes in this region include Mount Fuji in Japan, Mount St. Helens in the USA and Krakatoa in Indonesia. The 2011 Tōhoku earthquake and tsunami in Japan (magnitude 9.0) occurred along the Ring of Fire where the Pacific Plate subducts beneath the Eurasian Plate.
Scientists have gathered various types of evidence supporting plate tectonic theory:
The east coast of South America fits neatly against the west coast of Africa, suggesting they were once joined. This observation led Alfred Wegener to propose his Continental Drift theory in 1912, a precursor to plate tectonics.
Similar fossil remains of plants and animals (like Mesosaurus, a freshwater reptile) have been found on continents now separated by oceans, suggesting these landmasses were once connected.
Similar rock types and mountain ranges appear to continue across different continents. For example, the Appalachian Mountains in North America match up with mountains in Scotland and Norway.
As new rock forms at mid-ocean ridges, iron particles align with Earth's magnetic field. The pattern of magnetic reversals recorded in rocks on either side of mid-ocean ridges provides evidence of seafloor spreading.
Over Earth's history, the continents have repeatedly come together to form supercontinents and then broken apart again.
The most recent supercontinent, Pangaea, formed about 300 million years ago and began breaking apart about 175 million years ago. Before Pangaea, there were other supercontinents like Rodinia (about 1.1 billion years ago) and Columbia (about 1.8 billion years ago).
Scientists predict that in about 250 million years, the continents may form a new supercontinent called "Pangaea Ultima" or "Novopangaea." The Atlantic Ocean will likely continue to widen for about 100 million years before it begins to close as new subduction zones form.
The East African Rift Valley is an active divergent boundary where the African Plate is splitting into two parts: the Somali Plate and the Nubian Plate. This 6,000km-long system of rifts stretches from the Red Sea to Mozambique. The rift valley features steep fault-bounded walls that can rise 900m above the valley floor. Volcanic activity is common, with notable volcanoes including Mount Kilimanjaro and Mount Kenya. The rift is widening at about 2.5cm per year. If this continues, eastern Africa will eventually split from the main continent, creating a new ocean basin. This process demonstrates the early stages of continental break-up and provides a glimpse of how the Atlantic Ocean began to form when South America separated from Africa.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.