The Earth's Core

In Our Time: Science

BBC

History

4.5 • 1.4K Ratings

🗓️ 30 April 2015

⏱️ 47 minutes

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Summary

Melvyn Bragg and his guests discuss the Earth's Core. The inner core is an extremely dense, solid ball of iron and nickel, the size of the Moon, while the outer core is a flowing liquid, the size of Mars. Thanks to the magnetic fields produced within the core, life on Earth is possible. The magnetosphere protects the Earth from much of the Sun's radiation and the flow of particles which would otherwise strip away the atmosphere. The precise structure of the core and its properties have been fascinating scientists from the Renaissance. Recent seismographs show the picture is even more complex than we might have imagined, with suggestions that the core is spinning at a different speed and on a different axis from the surface. With Stephen Blundell Professor of Physics and Fellow of Mansfield College at the University of Oxford Arwen Deuss Associate Professor in Seismology at Utrecht University and Simon Redfern Professor of Mineral Physics at the University of Cambridge Producer: Simon Tillotson.

Transcript

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0:00.0	Thank you for downloading this episode of In Our Time, for more details about in our time, and for our terms of use, please go to BBC.co.uk.
0:09.0	I hope you enjoy the program.
0:11.0	Hello, it's said that we know more about the composition of the sun,
0:15.0	90 million miles away, than we do about the core of our own planet Earth.
0:19.0	It's only in the last eight years the scientists have moved towards a view that Earth has a solid inner core of mainly iron, the size of the moon, which is then surrounded by a larger liquid outer core, an ocean of molten metal, again mainly iron.
0:34.0	The edge of this core begins 3,000 kilometers beneath our feet.
0:38.0	Our going understanding of the core has helped explain the creation of the Earth's
0:41.7	magnetic field which shields this planet from the creation of the Earth's magnetic field which shields this planet from the
0:44.4	worst of the cosmic rays, so making life, as we know it, possible.
0:48.6	With me to discuss the Earth's core are Stephen Blondell, Professor of Physics and Fellow of Mansfield College at the University of Oxford.
0:56.0	Owen Deis, Associate Professor in Seismology at Utrecht University, and Simon Redfern, Professor of Mineral
1:02.4	Physics and Fellow of Jesus College at the University of Cambridge.
1:06.0	Stephen Nondale, let's start with the scientific journey to the centre of the earth in the 19th century
1:11.0	when people began to be interested in it. What did they know about it then?
1:15.0	Well in 1798 Henry Cavendish had measured the density of Earth. He'd done this by looking at the gravitational force between lead spheres, and this had
1:26.0	calibrated the strength of gravity. And he worked out that the density of Earth was about
1:31.3	five and a half times the density of water. Now why that was significant
1:35.2	is that the density of rocks is only about 2.5 to 3 times the density of water and
1:40.0	so if the Earth is just made of rocks there's something has gone wrong with the calculation
1:44.0	and it looks like to compensate that you need a much more dense core in the earth
1:49.7	and the density of iron is about eight times the density of water
1:53.2	iron is a very common material and so it seemed potentially logical that the earth
	...

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