Objective: To learn how tectonic plates move and what evidence we have for continental drift Tectonic Plates Starter: Word search – rock cycle review
Tectonic plates • The crust is made of about twelve plates. • These are like big rafts floating on the semi-molten mantle. • Convection currents within the mantle cause the plates to move. • Although they only move about 2 cm/year (same speed as fingernail growth) this can have huge effects over long periods of time.
Modeling convection currents • Put on goggles • Fill the beaker about ¾ full with water • Gently warm the beaker on one side with the candle • Using tweezers, place a crystal on the heated side of the beaker NB: The crystals will stain yourclothes and fingers
Convection current demonstration • Observe how the purple trails move around in a loop
Convection current demonstration • Observe how the purple trails move around the convection loop
Pangaea Millions ofyears Continental Drift • On average, the plates only drift about 2cm/year. However 2cm multiplied by a million years is a long way! • Scientists think the continents were originally all together in a super-continent called Pangaea. • Over millions of years they have drifted to their present positions on the floating tectonic plates.
Continental Drift People once thought that the oceans and the continents were formed by shrinkage from when the Earth cooled down after being formed. Alfred Wegener proposed something different: These continents look like they “fit” together. They also have similar rock patterns and fossil records. These two pieces of evidence led me to believe that there was once a single land mass.
Jigsaw fit Similar rocks and fossils Evidence for Continental Drift The theory is supported by several pieces of evidence. For example, if we consider Africa and South America there is: • The “jigsaw fit” • The similarities in the rock layers from Africa and South America. • Similarities in the type and age of fossils. • Evidence of related species that definitely did not swim the Atlantic Ocean!
Main Task • Write a memo from Alfred Wegener to a fellow geologist (scientist who studies rocks) • The memo should explain: • What is meant by continental drift • Evidence that proves the continental drift theory
Wrap up • 3 exam questions – class activity • In pairs, write 3 questions of your own that can be used as a quiz at the start of the next lesson
Q1 - The diagram shows the three main layers of the Earth. The middle layer is called the . . . . . crust. lithosphere. magma. mantle.
Q2 - The diagram shows the three main layers of the Earth. The middle layer . . . . . has convection currents which move very slowly. is made of solid rock which cannot flow. is made up of metamorphic rocks. is made up of sedimentary rocks.
Q3 - The diagram shows the three main layers of the Earth. The inner part of the inner layer (core) is . . . . . liquid and made from aluminum and silicon. liquid and made from iron and nickel. solid and made from aluminum and silicon. solid and made from iron and nickel.
Home work • How are natural disasters such as earthquakes/tsunamis linked to the movement of tectonic plates? • You should use the library/internet to research this HW • Aim to jot down at least 5 facts