Inside out
What would happen to the world as we know it if the Earth were hollow below the crust, assuming it didn’t collapse inwards?
• If the Earth were hollow we would be in danger of death by suffocation, thirst, frying, starving, freezing and drowning, in that order.
A hollow Earth would not have enough mass to hold on to an atmosphere by gravity, and all the surface water would boil away. If the crust had enough mass to make up for the hollow centre, there would be no magnetic field, which is generated by the Earth’s liquid iron interior. Compasses wouldn’t work, and some migratory animal species might get lost, but that would be the least of our worries as deadly radiation from the sun and outer space could then penetrate to the Earth’s surface.
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If this could be solved, then presuming we could grow gills we could live underwater. We’d need to, because within a million years the continents would have eroded to little more than sandbanks, and the sea level would rise because of all the sediment that was dumped in the ocean by the rivers. It is only subduction and mountain building, created by the same convection currents in the interior that create the Earth’s magnetic field, that keep uplifting the land to compensate for erosion.
Volcanic eruptions and subduction of tectonic plates also play an important role in regulating the carbon dioxide levels in the atmosphere. Without these processes, plant growth could cease entirely because of all the carbon reaching the ocean floor through erosion, and the Earth would enter a period of deep freeze, deprived of the essential warming effect – and food supply – that carbon dioxide gives us now.
Hillary Shaw, School of Geography
University of Leeds, UK
• A hollow Earth would weigh only about 5 × 1022 kilograms, roughly a hundredth of the present Earth.
The escape velocity for this new world would be about 40 centimetres per second, so the force required to jump to a height of just 1 centimetre on our normal Earth would send you hurtling into space. The same applies to our atmosphere: virtually all of it would have been lost as the gas particles acquired a velocity far greater than the escape velocity.
It would be a pretty grim world. There would be no spectacular volcanoes, and no source of lava. However, one could save time and money on flights from the UK to Australia by cutting holes on opposite sides of the globe and hopping through one of them – wearing protective clothing of course. The journey time would be a mere seven and a half hours.
Stephen Patrick Elliott
University of Cambridge, UK
• A hollow Earth would have been highly susceptible to destruction from the meteorites which bombarded the Earth in its early history. Even assuming it was not destroyed by the battering then it would be a barren place.
Without the heat, convection processes and source material of the core and the mantle there would be no tectonics and volcanism, therefore no atmosphere, no life and probably no water.
Laura Davies
Earth Sciences Department
University of Bristol, UK
Spice attack
Why does turmeric stain everything an indelible yellow, including surfaces that appear impermeable to other substances? Other powdered spices such as cinnamon, paprika and chilli do not leave the same legacy. And what is the best way to remove turmeric stains?
• Turmeric, the powdered rhizome of Curcuma longa, and paprika, which is obtained from the fruits of sweet peppers, Capsicum annuum, are examples of spices used in cooking as much for their colour as for flavour.
The yellow colour of turmeric is caused by curcumin, which makes up around 5 per cent of the dry powder. The red pigments in paprika are a mixture of carotenoids, principally capsanthin and capsorubin, and in dried paprika they amount to a maximum of 0.5 per cent of the weight.
The red carotenoids, which consist of long, chain-like molecules, are soluble in organic solvents such as petroleum spirit. Curcumin consists of smaller molecules with terminating phenyl groups. It is insoluble in water but dissolves in solvents like methanol. Therefore you might expect that both paprika and turmeric would stain paintwork and plastics, because they dissolve in organic solvents. You would also expect them to migrate to the oily part of food during cooking.
To compare their colouring properties, place a good pinch of turmeric into two small glass spice jars and do the same with paprika. Add a dessertspoon of methylated spirit to one set and the same amount of white spirit to the other (you can repeat the experiment with cinnamon and chilli powder). Upon shaking the mixtures you will see a vivid yellow colour appear instantly in the meths from the turmeric powder and the white spirit turn red from the paprika. When you place a drop of extract from each of the four jars onto a clean white plate, you will see that the turmeric-meths extract has much the strongest colour followed by the white spirit and paprika. The same experiment can be done with acetone (nail varnish remover).
This demonstrates the principal reason why turmeric stains more than other spices – it simply has more extractable colouring material in it. Other reasons will reflect the different physical properties of curcumin and the red carotenoids, as demonstrated in our solubility experiment, and differences in the way the dyes react chemically with solid materials. Drops of your extract can be placed on various surfaces to test their staining ability – but do ask first.
Curcumin is stable when heated but is not stable when exposed to light. So to remove a turmeric stain, first clean with methylated spirit and then place the object in sunlight.
Michael Elphick
Nottingham, UK
This week’s question
Life in a glass
How long can a human being live for if their sole source of food or drink is beer? And do different beers – ale, lager, stout, mild – confer a better chance of survival?
John Eden
Narara, New South Wales, Australia