Geologise! A journey to the centre of the Earth

How the structure and composition of the Earth's interior can be inferred without actually going there
Useful information
Kit List: 

Many rock samples (pumice, granite, basalt, peridotite, meteorites), Planet models, Volcano model with vinegar and bicarbonate of soda, light diffraction viewer, thin section microscope and camera, slinky, water tank and rod, apple, bar magnet and compass, electromagnet, convection tank with dye and heater

Packing Away: 

Return rock samples and thin section microscope and camera to the Earth Sciences department
Return any other equipment borrowed to the place of origin
Keep the rest for possible usage in other experiments


The audience form the crew of the Earth-ship GSS Geologise that will attempt to make a journey to the centre of the Earth. However, the vessel doesn't seem to work, so we're going to have to use different methods to work out what's going on beneath the surface of our planet (using a model of the Earth, uncovering the various layers when they are found). There also may be some music in the form of singing and playing on a keyboard, and lights flashing to evoke the impression of the ship working (or not as the case may be).

Rock Density:

The rocks at the surface of the Earth are much less dense than the average density of the Earth, so the core must be made up of a more dense material. Various rock samples will be used to illustrate this (none handled by the audience):

- Pumice: I large sample of a very low density rock that can be thrown up and headed (by the demonstrator) and can even float in water (use the water tank)
- Granite and Basalt: The constituents of the continental and oceanic crusts that have a relatively low density
- Peridotite: A rock from the mantle which is much more dense and brought up by volcanoes (possible volcano demonstration with vinegar and bicarbonate of soda and rolling of sleeve for ophiolites)
- Meteorites: Various kinds of meteorites that have a much higher density and imply that there is a dense core of iron (with an example of small planetary body models colliding) with the rest being made up mainly of silicates (talking about the Sun and how its composition can be determined through light diffraction)

Along with the hand samples the thin section microscope with a camera attached can show some of the minerals and forms in the different rock types.

Seismic Waves:

Earthquakes produce seismic waves that pass through the Earth and can be used to determine the structure of the planet. There are two kinds of body waves produced by earthquakes: P Waves (Primary/Push longitudinal waves) and S waves (Secondary/Sheer transverse waves). These two types can be demonstrated by a slinky or by member of the audience in a line holding onto the shoulders of the person in front, giving a gentle push forward for the longitudinal wave and a gentle sway for the transverse wave.

The seismic waves travel through the Earth and refract (shown by a rod in the water tank) leading to different paths. The P and S waves have shadow zones, implying that some of the core must be a liquid, with the centre being solid due to crystallisation, high density and certain ray paths.

The crust is found by certain waves travelling quicker on a higher density layer below, but is very thin (use an apple to show the scale).

Magnetic Fields:

The Earth has a magnetic field that helps us find our way (show a compass) and protects us from the solar wind (causing the Northern Lights) is a bit like a bar magnet, but not exactly as the poles wander, even switching over. The core is too hot to form a permanent magnet, so rather it could be a convecting liquid of a conductive material, such as the iron proposed before.

The water tank and a heater with some dye can be used to show a convection current, whilst the electromagnet can be used as an analogy of a self-exciting dynamo.

Possibly end with a song and the message that you don't always have to go to places to find out what's going on there.

Risk Assessment
Date risk assesment last checked: 
Thu, 11/02/2016
Risk assesment checked by: 
Date risk assesment double checked: 
Thu, 11/02/2016
Risk assesment double-checked by: 
Risk Assessment: 
Experiment Planet Model, Rock Samples, Microscope, Slinky, Apple, Magnets and Compass Music and Lights Seismic Waves Demonstration Water Tank Volcano Light Diffraction Viewer Electromagnet
Description Showing the samples to the audience with the only the pumice-head-butting and floating containing any risk Possibly some flashing lights and a song or too from a keyboard Audience volunteers hold shoulders of the person in front, being gently pushed or swayed Floating a rock or putting a rod in it, and also heating a bit of it showing the convection of a dye Volcano model which explodes with a vinegar and bicarbonate of soda reaction Audience member looks at a low-level light through the diffraction viewer Small example of an magnet turning in a magnetic field
  • Large but very light rock thrown up into the air and head-butted
  • Handling heavy rocks
  • Cables of microscope
  • Loud music
  • Bright flashing lights
  • Physical interaction
  • Cables
  • Liquids on electrical equipment
  • Heater getting hot
  • Spray from neutralisation reaction
  • Vinegar spillage
  • Strong lights
  • Cables
  • Electrical wires
  • Risks to audience
  • Risk if pumice stone is thrown and lands hitting audience (unlikely)
  • Damage to ears and eyes.
  • May cause seizures in people with photosensitive epilepsy.
  • Audience volunteers could push someone over
  • Audience volunteers could trip over wires
  • Fire risk
  • Sprayed with vinegar and/or bicarbonate of soda - irritant to eyes and cuts, and skin upon long exposure
  • Slip hazard from spilt vinegar
  • Damage to eyes
  • Tripping over cables
  • No risk
  • Risks to presenter
  • Damage head with pumice
  • Drop rocks
  • Splash water on electrical equipment
  • Damage to ears and eyes
  • Could trip over wires
  • Fire risk
  • Burns from heater
  • Drop rocks
  • Splash water on electrical equipment
  • Sprayed with vinegar and/or bicarbonate of soda - irritant to eyes and cuts, and skin upon long exposure
  • slip hazard from spilt vinegar
  • No risk
  • Electric shock
  • Battery may get hot
  • Control measures
  • Throw the rock to just above head height and don't hit it with much force. Ensure another committee member will be nearby, in case of injury to presenter.
  • Hold rocks carefully in two hands and place carefully back on the table
  • Keep the water tanks away from any electrical equipment and make sure there's no bare cables
  • Keep the music at a low sound level and the lights at a low level, warning people that there will be some flashing lights
  • Only gently push/sway the audience members and tell them to be very careful
  • Say to watch out for cables on the way to the floor and then make sure there are no cables in the demonstration area. Gaffa loose cables down if necessary
  • Keep the cables away from the water tank, but any that do need to be near, insulate
  • Don't touch the heater and keep it away from any flammable objects
  • Only use small amounts of vinegar and bicarbonate of soda
  • Point the volcano away from the audience
  • Have eyewash available
  • Keep the volcano in a container away from any electrical cables
  • Mop up any spillages promply
  • Only look into low level lights
  • Say to watch out for cables on the way to the floor and then make sure there are no cables in the demonstration area
  • Don't touch the wires
  • Don't leave on for extended time
  • In event of an accident
  • Clean up spilt water
  • Call first aider in event of injury
  • Call first aider if required
  • Call first aider in event of injury
  • Clean up spills.
  • Call first aider in event of injury.
  • Call first aider in event of injury
  • Parents may administer eye wash to child
  • Advise that vinegar and bicarbonate should be washed off skin
  • Call first aider in event of injury
  • Call first aider in event of injury
  • This experiment contains mains electrical parts, see separate risk assessment.