Earth's Structure and Plate Tectonics

• Earth formed 4600 million years ago and is constantly moving, though often just millimeters per year.
• The forces that cause Earth to move also lead to the formation of fold mountains, volcanoes, and earthquakes.

Earth's Structure

• Initially, Earth was liquid rock, but the outer surface cooled and hardened into a thin crust.
• The mantle lies beneath the crust, comprising 82% of Earth’s volume with a thickness of 2900 km.
• The mantle is liquid and flows, similar to hot jam.
• The outer core is an extremely hot liquid.
• The inner core is solid, with a temperature of 5500 °C, and located 6400 km from Earth’s surface.
• It took over a billion years for Earth's molten surface to cool and form the crust.

Plate Tectonics

• Earth’s crust is divided into large pieces called tectonic plates.
• There are 7 major tectonic plates, some larger than continents.
• These plates are in constant motion, rubbing against each other, colliding, or moving apart.
• Plate boundaries (or margins) are the edges of these plates.
• Most of the world’s volcanoes and earthquakes are found at plate boundaries.
• Plates consist of continental and oceanic crust.
• Continental crust is light, strong, cannot sink, and cannot be destroyed.
• Oceanic crust is heavier, can sink under continental crust, and is continually destroyed and replaced.
• Plates move because they float on the extremely hot mantle.
• The mantle consists of liquid magma, and intense heat from Earth's core causes convection currents.
• Convection currents push under the plates, causing them to move.

Types of Volcanoes

• Volcanoes are classified by their activity level: active, dormant, or extinct.
• Active volcanoes erupt frequently.
• Dormant volcanoes are not currently erupting but could in the future.
• Extinct volcanoes are highly unlikely to erupt again.

Volcano Structure

• Volcanoes are composed of ash, bombs, vents, lava, gases, a crater, side crater, cone, and a magma chamber.
• Main parts include the ash cloud, layers of lava/ash, magma chamber, main vent, secondary vent and crater.

Volcano Shapes

• Volcanoes are also categorized by shape and composition: shield and strato/composite volcanoes.
• Shield volcanoes are low with gently sloping sides, formed from thin, runny lava, and have fairly frequent, gentle eruptions.
• Strato/composite volcanoes are mainly made of lava with alternating layers of ash, and can have very violent eruptions.
• Pyroclastic flow is a mix of hot steam, ash, rock, and dust flowing down mountain sides at speeds of temperatures up to 400°C.

Plate Boundaries

• Plate boundaries, or margins, are the edges of tectonic plates.
• Recent earthquakes and volcanoes are located on the edges of plates.
• Constructive/diverging margins occur where two plates move away from each other.
• Molten rock (magma) rises from the mantle to fill the gap, forming new oceanic crust.
• The process at constructive margins is also known as sea-floor spreading.
• The mid-Atlantic ridge is widening at about 3 cm a year, increasing the distance between Europe and the Americas.
• Earthquakes and volcanoes occur at constructive margins.
• Destructive/converging margins are where plates containing oceanic crust move towards plates containing continental crust.
• The heavier oceanic crust is forced under the continental crust in a subduction zone.
• Friction and increased temperature cause the crust to melt.
• The newly formed magma might rise to the surface, forming volcanoes.
• Increased pressure from the downward force can also trigger severe earthquakes.
• Conservative margins occur where two plates slide past each other, often at different speeds.
• Conservative margins does not form any new landscape.
• There is no volcanic activity at conservative margins.
• Earthquakes can occur at conservative margins if the plates get stuck.
• Pressure builds up until released, causing the Earth to jerk violently. An example is the San Andreas Fault in California.
• Collision margins involve two plates of continental crust moving towards each other.
• Collision margins forms fold mountains.

Explore Earth's structure, from its crust and mantle to its liquid and solid core. Discover the concept of plate tectonics, including the major plates and their constant movement, which shapes our planet.