Four Revolutions in the Earth Sciences by James Lawrence Powell

four revolutions in the earth sciencesThe weight of evidence…

😀 😀 😀 😀

In the introduction, Powell tell us he was inspired to write this book when a friend, discussing the fact that the vast majority of scientists accept that the activities of man are contributing to global warming, remarked that scientists have been wrong before. Accepting the undeniable truth of that, Powell decided to look at the recent history of four important theories in earth sciences, showing that though scientists may have been wrong at first, they “eventually came to be right”.

The history of the four discoveries confirms the cardinal virtue of science: it is self-correcting. Scientists pushing the boundaries of knowledge are often wrong, but they do not stay wrong.

Considering the fair amount of depth Powell goes into on each of his subjects, the book is surprisingly accessible to the non-scientists among us. I found I only got lost occasionally and, when reading books like this, I accept that there are things that are too complex to simplify down to my level! In each section Powell starts at a point before the theory he is discussing was developed, explaining the existing state of knowledge and supposition. He then introduces us to the scientists who contributed to the development of the new theory, along with those who opposed it, and finally to those who ‘proved’ it. He provides little anecdotes of their lives, or their friendships or quarrels with each other, which prevent the book from becoming too dry a read.

James Larence Powell
James Lawrence Powell

There are two types of enjoyable popular science books as far as I’m concerned – those that clearly explain something and convince me of it, and those that clearly explain something and provoke me to argue with the author’s conclusions. This one falls firmly into the latter category. Oddly, I started out a fairly firm believer in all four (five really, or six if you include the extinction of the dinosaurs) of the theories in the book, and ended up only fully convinced of two – or two and a half at a push. Throughout, Powell is critical of scientists who accepted theories and held onto them despite lack of proof or even once discoveries had been made that clearly invalidated them. But I felt Powell fell into that same trap himself too often, claiming a thing as being so when in fact the proof isn’t yet there. The very subtitle of the book – From Heresy to Truth – is a prime example of this. His basic position seems contradictory – that scientists of old were stubborn and foolhardy to stand by their theories without adequate proof but that we should accept the theories of current science, also often without final evidence of their validity. And he makes generalized statements that are clearly an expression of his opinion rather than of ‘fact’…

The discoveries from astronomy and earth science expose the infinitesimal standing of the human race in time and space. They force us to admit that we are the products of, and the potential victims of, random events.

Do they really? I would imagine that the billions of people who believe in some form of God might not feel forced to admit that. Indeed, Powell himself points out in the course of the book that even many scientists are willing to admit that science and religion can co-exist. But this is just one example – there were several occasions when I felt he expressed himself more forcefully than the evidence justified, or substituted opinion for fact.

Continental Drift
Continental Drift

However, despite finding I was treating his conclusions with some caution, I found the book interesting and informative, and felt that overall he more or less made his case. Perhaps had he been a little less ambitious to prove the rightness of so many current theories, he might have been more convincing overall. Here is a brief summary of the theories he discusses…

Deep Time

Powell shows how the assumed age of the Earth has changed over the last century or so, as scientists made discoveries – such as evolution – that negated the previous assumptions. As he does in each section, he highlights the scientists involved, including those who fought strongly to retain their existing position even when the evidence became overwhelming. He also points out that, in the end, it was physicists rather than geologists who made the most important discovery – how to determine the age of rocks through developing ways to measure radioactive decay.

My verdict: Not proven – an old Scottish verdict which means basically ‘I believe it, but I don’t think you’ve really proved it’. I admit the main reason for this verdict is that the stuff about radioactive decay went largely over my head – but it seemed to me that, as Powell described it, there were still too many assumptions involved for this to be a theory incapable of being overturned by further future discoveries.

Giant Impact Hypothesis for creation of the Moon Pciture credit: National Geographic
Giant Impact Hypothesis for creation of the Moon
Picture credit: National Geographic

Continental Drift and Plate Tectonics

In 1911, Alfred Wegener noticed that the east coast of South America was a great fit for the west coast of Africa, and speculated that they had once been joined. The then greats of the scientific world largely dismissed this idea, even when the fossil records between the two coasts showed a remarkable similarity. Powell takes us through all the experimentation that gradually proved the truth of the theory, as geologists speculated that continental drift and plate tectonics were the likely cause of mountain formation and of the mid-Atlantic ridge.

My verdict: Proven. With GPS, scientists have now been able to measure the rate of drift – that’s the kind of proof I like!

Meteorite Impact

While discussing the theory that meteorites have impacted the Earth, on occasion with catastrophic results, I felt Powell got himself a bit side-tracked into both the extinction of the dinosaurs and the impact theory for the creation of the Moon.

My verdict – the jury is still debating. I don’t think any of us who watched Shoemaker-Levy 9 crash into Jupiter some years back could doubt that major meteor strikes happen, nor be unconvinced of their catastrophic potential; and I was convinced of the evidence that they have happened here on Earth. However I felt Powell’s certainty that this was the cause of the extinction of the dinosaurs was too strongly expressed – again, I tend to believe it, but don’t think it has been ‘proved’. And as for the Moon creation theory, even Powell had to admit that this one needs much more evidence before it moves from theory to fact. (Oddly enough, I thought that one had been proved – Powell unconvinced me.)

Dinosaur extinction Credit: Mark Garlick, Science Photo Library Photo??? It must be true, then...
Dinosaur extinction
Credit: Mark Garlick, Science Photo Library
Photo??? It must be true, then…

Global Warming

So this is the crucial one – Powell’s starting and finishing point. Although he refers to it as Global Warming, in fact the crux of his argument is proving that it’s caused in large part by man’s actions. Again this one got a bit ‘sciency’ for me, but for the most part I was able to follow the arguments.

My verdict: Proven. It seems to me the weight of measurable evidence – such as from atmospheric measurements over time showing the rapid rise in concentration of carbon dioxide to be almost exactly parallel with the increase in emissions – makes this one as close to proven as it’s likely to be. And given the potential impact, I’d rather err on the side of caution anyway. But, although Powell’s position is that this one is beyond doubt, he also makes it clear that estimates of the likely impact are still subject to debate. Personally, I feel we’re probably safest to assume a worst-case scenario and act accordingly…and on that final note, I think Powell and I finally reached agreement.

An interesting book, despite Powell’s occasional forays beyond the evidence, and one I would recommend to anyone who is still in doubt as to the reality of man’s impact on the environment.

NB This book was provided for review by the publisher, Columbia University Press.

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