The Earth's heat comes from events which happen:

• During formation - extra-terrestrial impacts, gravitational contraction and frictional heating

• Currently - radioactive decay

Heat moves around:

• In the outer core, where moving liquid iron and nickel create the Earth's magnetic field

• In the mantle, with rising hotter material and sinking colder material   

The geothermal gradient is raised at hotspots, divergent plate boundaries and close to volcanoes. This can be used for geothermal energy.

There are two sources of geothermal energy:

• hot rock geothermal

• groundwater

The heat can be used to generate electricity or provide heating via hot water. The energy is renewable, closed-loop and can provide energy security for regions with access to geothermal heat. However, it is geographically restricted and the energy that can be produced at one time is restricted.

The Earth's crust is broken into plates, which are moving around in different directions. 

(The SQA say that the movement is caused by convection currents. This is outdated and it's now understood to be driven by sinking slabs of oceanic crust and rising ridges at divergent plate boundaries).

The boundaries between plates can cause natural hazards and are often the source of minerals we can utilise (e.g. metals). There are different types of boundaries:

• Divergent (constructive) boundaries - where two plates are moving away from each other, creating a space for magma to rise. This creates underwater volcanoes and hydrothermal vents.

• Convergent (destructive) boundaries - where two plates are coming together, causing the denser plate to subduct. This carries oceanic sediments and seawater which lowers the plate's melting point and generates magma. The magma can contain concentrated metallic minerals. A deep-ocean trench, mountain chains and explosive volcanoes are also associated with these plate boundaries.

There are three main types of rocks in our crust:

• Igneous rocks which form from molten magma. Called intrusive rocks where they cool underground (e.g. granite) and extrusive where they have been erupted as magma (e.g. basalt).

• Sedimentary rocks formed from eroded and deposited sediments such as sandstone, siltstone and mudstone.

• Metamorphic rocks which have formed under intense heat and pressure. Examples include gneiss and marble.

Bauxite is a sedimentary rock which forms when rocks high in aluminium oxide are chemically weathered. Many of these original rocks are associated with subduction zones.

Areas with high temperatures and rainfall can undergo extreme chemical weathering (e.g. equatorial regions). Nutrients are leached out of the soil, leaving it concentrated in aluminium oxides.

Most bauxite is extracted using open cast mines. Environmental issues include:

• removal of vegetation

• erosion and runoff

• pollution

• waste products (overburden and tailings)

Bauxite is processed to obtain the useful metal by smelting. This:

• requires very high inputs of electricity, water and resources

• releases greenhouse gases

• produces red mud as a waste product

• involves transporting bauxite long distances to smelting sites

Water is moved by:

• evaporation

• condensation

• precipitation

• infiltration

• percolation

• transpiration

• evapotranspiration

• sublimation

• runoff

Water is stored at the surface as:

• atmospheric moisture

• snow

• ice

• watercourses

• lakes

• oceans

Water is stored underground as groundwater or in aquifers.

SEPA is the key environmental agency in Scotland responsible for monitoring river and loch levels.

Hydrographs show the response of a river to a rainfall event. 

Hydrographs can be described by referring to:

• peak rainfall

• peak discharge

• lag time

• base flow

Different factors may change the shape of a hydrograph, including how much water in the basin has travelled as surface run-off, soil water or groundwater.

Flooding can be reduced by:

• Planting  vegetation, which slows down runoff increases vegetation storage.

• Storing of water upstream including dams and weirs

• Removing impermeable surfaces (e.g. tarmac)

Deep ocean currents move in a system called the global ocean conveyor belt. 

This is driven by the formation of ice at the poles which leaves cold, salty water which sinks and travels in the deep ocean. This is called thermohaline circulation.

Eventually, the cold bottom water returns to the surface through mixing and upwelling. Upwelling brings nutrients from the deep ocean to the surface, which supports marine food chains.

Surface ocean currents (e.g. Gulf Stream) are influenced by global wind patterns, which drag on the ocean surface. The rotation of the Earth causes the Coriolis effect, which defects these to the right in the Northern Hemisphere. The currents create loops (gyres) which are found north and south of the equator.

Marine litter can get trapped in the centre of gyres.

Factors which affect oceanic circulation include:

• thermohaline circulation

• continental location

• surface winds

• Coriolis effect

There are 5 inputs to soil formation:

• relief

• climate

• parent material

• organisms

• time

The interaction of these will create different soil profiles.

Processes involved in the formation of soils include:

• physical, chemical and biological weathering

• decomposition and humification

• translocation of material via leaching, eluviation, illuviation and capillary action

Soils are composed of:

• Mineral matter from rocks (soil texture)

• Air & gases from the atmosphere and reactions in the soil (pore spaces)

• Water from the atmosphere and reactions in the soil

• Organic matter from decaying plants and animals

The proportions of the above have an impact on the soil structure, texture, ability to retain water and nutrients, drainage, aeration and resulting land use.

Organisms found in a soil include:

• macro organisms (worms, insects)

• micro organisms (bacteria)

First generation biofuels are created from edible sources:

• bioethanol from distilled fermented sugar 

• biodiesel from animal fats or vegetable oils

Second generation biofuels are created from non-edible sources:

• Biomethanol from waste products in the forestry and industrial sectors; decaying landfill

• Bio-crude oil from heating biomass to replicate natural processes (i.e. formation of oil over millions of years).

Biofuels are:

• Renewable

• Carbon neutral

• A way to use up waste products

• Often able to be used with existing engines 

• A source of energy security for countries with few conventional resources

• A cause of deforestation

• Grown using lots of chemical fertilisers

• A threat to food prices

• A threat to water security

The atmosphere is composed of:

• Nitrogen

• Oxygen

• Argon

• Carbon dioxide

• Methane

• Water vapour

and small amounts of other gases

The Global Heat Budget is the balance between incoming and outgoing solar radiation. 

Insolation varies at different times of the year (e.g. winter) and at different latitudes (e.g. because of the tilt of the Earth).

Energy is absorbed by the atmosphere and Earth's surface. It is also reflected by the atmosphere and Earth's surface.

Reflection of solar energy is called albedo. Surfaces can either have a low albedo (0 = no reflection) or high albedo (1 = 100% of energy is reflected). 

• Low albedo surfaces include forests, oceans and deserts. 

• High albedo surfaces include snow and ice.

Tropical regions have high insolation and polar regions have low insolation. The atmosphere & oceans redistributes this energy to maintain balance.

The three-cell model explains how this is done in the atmosphere:

• Hadley, Ferrel and Polar Cells - these move warm and cold air

• Surface winds - these are the expression of the cells on our surface

• Coriolis effect - this causes the winds and ocean currents to be deflected - right in the N hemisphere.

The low and high pressure created by rising and sinking air cause biomes. These are regions with similar climatic conditions and associated habitats, plants and animals.

• High atmospheric pressure - hot desert, tundra

• Low atmospheric pressure - rainforest (equatorial and temperate)