TOPIC 1:TECTONIC PROCESSES AND HAZARDS (Lesson 2)

1. Why are some locations more at risk from tectonic hazards? ENQUIRY QUESTION 1: 1. Why are some locations more at risk from tectonic hazards?

SPECIFICATION REQUIREMENT 1.2 a) The theory of plate tectonics and its key elements : ( the earth’s internal structure, mantle convection, palaeomagnetism and sea floor spreading, subduction and slab pull.)

Lesson Objectives: To understand the key elements of plate tectonics To have knowledge of the internal structure of the earth as we know it……!

What is the centre of the earth called? What is it made of? How far is it to the centre of the earth? What is the crust made up of? http://www.youtube.com/watch?v=QDqskltCixA https://www.youtube.com/watch?v=Kg_UBLFUpYQ ( 15 min intro to plate tectonics- show first 3.45 mins: N.B PLATES DON’T FLOAT!)

So what’s it like inside then?

The Structure of the Earth: p.7 Three basic layers: Core (split into two: inner and outer core) Mantle Crust

http://www. bbc. co. uk/learningzone/clips/structure-of-the-earth/9117 http://www.bbc.co.uk/learningzone/clips/structure-of-the-earth/9117.html

HOW DO WE KNOW ? So….since the centre of the earth is so hot (@5500 degrees C but some scientists believe that it is more like 6000!) this means that scientists can’t drill into it. Instead they map it by using evidence from seismic waves ( shock waves released by tectonic movements- see later notes on this…)

The Core Centre of earth 6371 km below surface Density 12 g/cm³ Size of mars Temperature approx 5500 C Divided into inner and outer core: Inner core: solid, due to pressure and weight of all the other layers(mostly iron) (N.B In 2015 seismic –wave data suggested that the inner core now has another distinct area at ts centre ‘the inner inner core’ !) Outer core: semi molten (mostly liquid iron and nickel)

The Mantle Extends to depth of 2900km Temperatures up to 5000 C The lower mantle is solid and the upper mantle is also solid but shows ‘plastic’ properties ( like a half melted bendy mars bar!) Rocks contain lighter elements containing oxygen and silicon ( main rock is ‘peridotite’) Convection currents have been thought to exist and transfer heat around this layer…….. ( N.B Contested theory- see later notes!)

The Crust Surface layer of the earth Relatively speaking it is as thin as the skin of an apple is to its flesh Lower density as many lighter elements are present in the rock- silicon, oxygen, aluminium, potassium, sodium Varies in thickness from 6-10km below oceans, to 30-40km under continents, up to 70km under highest mountain ranges Two types of crust exist:

The Crust Continental Crust (which underlies the continents) This is where we live! The Earth’s crust is made of: Continental Crust (which underlies the continents) Oceanic Crust ( which lines the ocean floors) The Earth has two different types of crust: Continental crust and Oceanic crust. Each has different properties and therefore behaves in different ways. Continental crust: Continental crust forms the land (the continents, as the name suggests) that we see today. Continental crust averages about 35 km thick. Under some mountain chains, crustal thickness is approximately twice that thickness (about 70 km thick). - The mountains we see on earth have deep roots in the crust that we can’t see. The crust “floats” on the more dense mantle and, like how only the tip of an iceberg sticks up out of the water, we see only the tip of the continental crust - the mountain ranges. Continental crust is less dense and therefore more buoyant than oceanic crust Continental crust contains some of the oldest rocks on Earth. - Ancient rocks exceeding 3.5 billion years in age are found on all of Earth's continents. The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) [Ga = billion years ago] and the Isua Supracrustal rocks in West Greenland (3.7 to 3.8 Ga), but well-studied rocks nearly as old are also found in the Minnesota River Valley in the USA (3.5-3.7 billion years), in Swaziland (3.4-3.5 billion years), and in Western Australia (3.4-3.6 billion years). Oceanic crust: As the name already suggests, this crust is below the oceans. Compared to continental crust, Oceanic crust is thin (6-11 km). It is more dense than continental crust and therefore when the two types of crust meet, oceanic crust will sink underneath continental crust. The rocks of the oceanic crust are very young compared with most of the rocks of the continental crust. They are not older than 200 million years.

Continental Crust Oceanic Crust Thicker, 10- 70km Over 1500 million yrs old ( older) Density 2.6 g/cm³ (lighter) Mainly granite: silicon, aluminium, oxygen (SIAL) Thinner, 6-10km Less than 200 million yrs old (younger) Density 3.0 g/cm³ (heavier) Mainly basalt: silicon, magnesium, oxygen (SIMA)

WHITEBOARD RECAP STARTER QUESTIONS 1. A perceived natural geophysical event that has the potential to threaten life and property is? A HAZARD 2. Give three examples of tectonic hazards EARTHQUAKES, VOLCANOES, TSUNAMIS 3. What overriding factor makes these hazardous? PROXIMITY TO PEOPLE 4. How do scientists know about the structure of the earth? By mapping it from seismic waves and from geological surveys…

5. What can be found approx. 6371 km below the earth’s surface? THE CORE 6. What is the approximate temperature of the core? 5500/6000 degrees C 7. Which is solid – the inner or outer core? INNER 8. Why? Due to pressure and weight from all the other layers on top 9. The lower mantle is solid but what is the upper mantle like? SOLID WITH PLASTIC PROPERTIES 10. What is the name of the surface layer of the earth? CRUST

11. Name the two types of crust OCEANIC AND CONTINENTAL 12. Which is denser? OCEANIC CRUST 13. Which is thicker? CONTINENTAL CRUST? 14. Which is older? CONTINENTAL CRUST 15. Which is composed of mostly basalt?

Lesson Objectives: To understand the key elements of plate tectonics To have knowledge of the internal structure of the earth as we know it……! https://www.youtube.com/watch?v=Q9j1xGaxYzY

Task: Fill in your world plates map on page 11 (Ref Edexcel Book 1 fig 1.1 p 3)

Add the following plate names to the map. Pacific plate, African plate, Eurasian plate, Australian-Indian plate, Antarctic plate, North American plate, South American plate, Nazca plate, Phillipine plate, Caribbean plate, Cocos plate, and Juan de Fuca plate.

? Eurasian plate African plate Antarctic plate Pacific plate Juan de Fuca plate Eurasian plate North American plate ? Phillipine plate Caribbean plate Pacific plate Cocos plate African plate South American plate Australian-Indian plate Nazca plate Antarctic plate Add the following plate names to the map. Pacific plate, African plate, Eurasian plate, Australian-Indian plate, Antarctic plate, North American plate, South American plate, Nazca plate, Phillipine plate, Caribbean plate, Cocos plate, and Juan de Fuca plate.

What is a plate? A plate is a piece of the earth’s rigid lithosphere. ( N.B Since the lithosphere is made up of crust and the top part of the mantle it is NOT correct to say that a plate is merely a piece of the earth’s crust!!!!) WATCH OUT!! The plate sits on top of the asthenosphere below and moves about by the underlying plastic asthenosphere.

DRAW A LABELLED DIAGRAM OF THE EARTH’S INTERNAL STRUCTURE TASK DRAW A LABELLED DIAGRAM OF THE EARTH’S INTERNAL STRUCTURE (p.8)

More recent ideas…P.9 3 layers idea too simplistic and the upper layers are more complex…… 1.LITHOSPHERE: The crust and the upper part of the mantle act as a single unit, a layer we call the ‘lithosphere.’ It is about 80km thick, is rigid and brittle It is divided into pieces called plates; 7 very large ones and a number of smaller ones. 2.ASTHENOSPHERE: Below the lithosphere is the ‘asthenosphere’ .This is about 200km thick layer and here the rocks( mostly peridotite) are solid but plastic and capable of flowing. The rigid material of the lithosphere sits (not floats as previously thought!) on the plastic asthenosphere and moves approx 5cm a year,allowing the plates to move about.

Recent ideas cont.. The outermost skin of the lithosphere is either the oceanic or continental crust which is separated from the mantle lithosphere by the ‘Moho discontinuity’.

The ‘Moho’ separates the crust from the upper mantle ( or ‘mantle lithosphere’). It is a term denoting a change in physical properties with increasing depth.

PLENARY On a piece of paper write down 3 facts that you have learnt from this lesson. Turn them into quick questions with answers. Test your neighbour!

H/W 1. Complete notes on the recent Italian earthquake Aug 24th 2016 2. Make sure that all notes / diagrams/ maps from this week’s lessons are complete 3. Revise all key terms for a quick test at the beginning of next week’s lesson DON’T FORGET TO CHECK WEEBLY!!