Can you touch anywhere on your body with your right hand? Replying quickly, you might say you can. But what about your right elbow? You can’t touch that with your right hand. Science is like that, because distant things are often easier to study and understand than close things. We have a good understanding of how stars work, for example, but not of how the earth’s magnetic field is generated.
And while we’ve been able to predict solar eclipses for millennia, we still can’t predict earthquakes or volcanic eruptions. Understanding the deep earth is difficult, so there are a lot of mysteries and conjectures in this well-written and compelling book about the interior of our home planet. Scientists have landed probes on Mars, millions of kilometres away, but the “deepest hole ever drilled on earth – the Kola Superdeep borehole in northern Russia” reached only 12,262 metres. That’s a mere pinprick by comparison with the radius of the earth. To get beyond that, scientists have had to study the shockwaves generated by earthquakes. The medium is the message: as the waves pass through or hit different regions and materials, they behave in different ways.
For example, when the Croatian scientist Andrija Mohorovičić (1857-1936) “studied the records from several seismometers” after an earthquake near Zagreb, “he realised that some of the shockwaves […] were being reflected back to the surface from a boundary region between the crust and mantle.” (pg. 82 of the 2016 paperback) The region is now called the Mohorovičić discontinuity. But that discovery was made before the First World War and deep geology hasn’t advanced very much in the intervening century. This book borrows the title of a Jules Verne novel published in 1864. If Verne came back to life, he would be pleased to see that his work is still popular, but he would be disappointed to see that the human race was no nearer reaching the centre of the earth.
Or would he? The American geologist Don Anderson says: “Almost everything known or inferred about the inner core from seismology or indirect inference is controversial.” (pg. 211) Deep geology is a difficult science, but that’s part of what makes it so interesting. Something else that makes it interesting is that the inner earth can visit catastrophes on the outer earth and the film of the life that clings there:
The big question is: can we see mass extinction events on the way up? Some scientists believe that we can by looking for the plumes [i.e., giant plumes of rising magma]. Such a thing is seen in the south-west Pacific near the Fiji Tonga subduction zone. It’s 700 km deep, has a structure consistent with a massive temperature anomaly and may be rising. It could render the earth uninhabitable for humans and it will reach the surface in an estimated 200 million years. (ch. 17, “Plumes”, pg. 146)
Asteroid impact and gamma-ray bursts are not the only catastrophes that threaten the continued existence of the human race. They may not even be the most likely. The film of life on the surface of the earth is fragile and one day it won’t be there any more.
But there’s also life deep inside the earth, living in conditions of extreme pressure, heat and darkness. We still know little about this “deep biosphere” and it may hold some big surprises. The rest of the deep earth almost certainly does. And the deep earth is just the beginning: as Whitehouse describes in chapter 26, there are “Other Worlds, Other Journeys” to come, including the even more extreme conditions at the heart of Jupiter, where the temperature is a “staggering 37,000 degrees C” and the pressure is “over ten times that found at the centre of the Earth.” (pg. 239)
Or so scientists estimate. Will scanners be invented to prove their theories? Will probes ever get there and find out for real? We can hope so. In the meantime, this book is an excellent introduction to the ideas, the pioneers and the modern researchers into mysteries that are right beneath our doorsteps. Whether it’s discussing diamonds, demons or “Double-D-Prime”, Journey to the Centre of the Earth is popular science that’s interesting, entertaining and informative all at once.