It’s 6,378 kilometres from the surface of the Earth to its centre. That distance was important for Professor Von Hardwigg when he embarked onA Journey to the Centre of the Earthin the 1864 novel by Jules Verne.
But for prairie farmers, all they’re really interested in is the top couple of metres, especially the top 20 to 30 centimetres.
That’s the Earth’s topsoil.
It’s too thin a layer to show up on cut-away diagrams of the Earth’s structure, but it’s crucial to the production of crops and other cultivated plants and the survival of trees, grasslands and other wild flora.
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“Our agriculture depends on the top few feet of the earth’s surface,” said Darwin Anderson, a soil scientist at the University of Saskatchewan.
“Most plants put their roots down to three or four feet (90 to 120 cm) so it’s the top metre or two that’s important for farmers.”
Topsoil is generally a darker colour than other soil, reflecting the greater concentration of organic matter. It also contains the nutrients and microorganisms necessary for the efficient production of plants.
Anderson said the thickness of topsoil varies widely, not only between different geographical regions but also within fields.
On hilly land, for example, there will generally be less topsoil on the tops of knolls or hills and much more at the bottom, the result of soil moving down the slopes over hundreds of years as a result of natural or human forces.
Topsoil depth ranges from 10 to 15 cm in the drier areas of Saskatchewan to 20 to 25 cm in more moist areas such as southern Manitoba, southeastern Saskatchewan and central Alberta.
Topsoil is formed over hundreds or thousands of years as plant material breaks down into organic matter, replete with nutrients and microorganisms.
Topsoil depth hasn’t changed much since the glaciers retreated 10,000 to 15,000 years ago and the process of soil formation began.
Directly beneath the topsoil is a layer known as subsoil, which contains much less organic matter, fewer nutrients and microorganisms and doesn’t have the same ability to support plants.
Beneath that is the bedrock, the first layer of solid rock underlying the soil, sand, loose glacial deposits, volcanic ash or sediments. Depending on the specific location, bedrock could be granite, basalt, limestone, sandstone or gneiss.
The bedrock has no impact on the quality of the topsoil above.
The outer core, at a depth of 2,900 to 5,150 kilometres, is composed of liquid iron and nickel with temperatures ranging from 4,000 to 6,100 C. The inner core represents the final 1,220 km to the centre, a solid sphere of extremely hot iron-nickel alloy between 5,000 and 7,000 C.
JULES VERNE’S FANTASTIC JOURNEY
So what about Professor Von Hardwigg and his fictional journey to the centre of the Earth?
In the book, the professor, accompanied by his nephew and a guide, follow an ancient coded manuscript and travel into an extinct volcano in Iceland, hoping to find a way to the centre of the Earth.
Along the way, the trio encounters a variety of adventures, including prehistoric landscapes, giant insects, mastodons and a giant human skull. The explorers are eventually caught in a raging river and expelled through the side vent of an active volcano in southern Italy.
Van Hardwigg failed in his quest but returned to a hero’s welcome in his native Germany.
