We do not have enough data from other star systems to know whether our solar system is typical or atypical. Perhaps solar systems such as ours are two a penny, or perhaps ours is the consequence of a set of highly specific circumstances that have never been repeated. The study of exoplanets – planets orbiting other stars – reveals that planets are common, and planets of a similar size to Earth that orbit around stars at a distance where water, a key chemical for life, exists as liquid, are likely not particularly rare. Many Earth-like planets may exist, but that does not mean we are not unique. Earth’s history is important on the journey from the Big Bang to you and me, and to study it we have to piece together our planet’s history using all the tools of the scientific method. At this point, I take a slight detour from the history of our planet to explain the next bit of my history of becoming a scientist.
I found the science taught at school was largely uninspiring, and things didn’t immediately improve when I headed to university in the delightful Cathedral city of York in the north of England. I loved university, but many of the lectures left me bored, and I continued to largely self-learn in the library. I enjoyed reading papers published in scientific journals. In one lecture in the second year of my biology course, a friend and I were sitting at the back being disruptive. We were chatting a bit too loudly and flicking balls of paper at our friends. At the end of the lecture we were asked to remain behind so the professor, John Lawton, could tell us off.
I felt mortified, so later that day I went to Professor Lawton’s office to apologize. He asked me why I had been fooling around, and I explained that I didn’t feel challenged by the lectures and that the contents of the scientific papers I was reading seemed much more nuanced. Professor Lawton told me I was right but that we had to be taught the basics, which was fair enough, and that I should hang in there as I would find the research projects of our final year much more stimulating. He proved right, but I never saw him at York again, and I quickly forgot about my telling-off.
A year later, with the end of my undergraduate course approaching, I needed to decide what to do next, and, other than understanding why I existed, I really had no idea what I wanted to do. My then girlfriend was applying to do a Ph.D. at Imperial College London, so I decided to apply too. I didn’t have a clear idea of what graduate studies might entail, but I put a lot of effort into my application and sent it off. A few weeks later I was invited to interview, and the letter informed me that I would be interviewed by Professors Mick Crawley and John Lawton. My heart dropped. Professor Lawton would recognize me, remember my disruptive behaviour, and that would be game over for my hope of graduate studies at Imperial. Except it didn’t play out like that. John, as I came to know him, greeted me with a ‘hello again, Tim’ before explaining there was no need to mention our past interaction. The interview went well and I was offered a place. John had remembered me from our conversation and had been impressed with my comments about the lecture content and my extracurricular reading. I wouldn’t recommend mucking around in class, but on that occasion it paid dividends.
John and Mick felt I should also be advised by Professors Charlie Canham and Steve Pacala for part of my Ph.D. that involved data collection from a large project the two Americans ran in the north-east of the United States. I didn’t realize it at the time, but John, Mick, Charlie and Steve constituted a dream team of scientific mentors, not only for their stellar track records but also because they each took a different approach to their science. John is an all-rounder: an exceptional naturalist with a deep understanding of how the natural world works. He would frequently tell me to ‘take a step back and think about the big picture’ when I got caught up in the minutiae of my own project. I doubt he ever imagined I would take quite so many steps back to write this book. Mick studies plants and is an expert in how to use statistical approaches to analyse biological data to test hypotheses. He is also a talented teacher, being able to enthuse the innumerate about statistics. Charlie is a forest ecologist who studies nutrients and energy flow through food webs, and Steve is a theoretician who builds and analyses models to acquire general insight.
A little bit of each of their approaches rubbed off on me, and I developed into a science all-rounder rather than a champion of any single element of the scientific method. Their mentorship also taught me that good scientists are imaginative but can discard promising ideas that violate existing understanding, can alter their opinions when data shows a cherished hypothesis is wrong, and are evidenced-based and constructively critical. Science has been said to advance one funeral at a time, because many scientists will not give up strongly held beliefs even in the face of overwhelming evidence, but my mentors showed me that didn’t need to be the case. Mick used to reject a hypothesis annually. After finishing my Ph.D. I worked with him and other collaborators on a remote Scottish island that was home to a population of wild sheep. Each year we would have a bet on the number of sheep alive on the island before counting them, and I developed a predictive mathematical model that worked reasonably well. Predicting the future was not Mick’s greatest strength, but he would cheerily accept his hypothesis was wrong and grudgingly pay up. He did well to choose science as a career, as he’d not have excelled as a Wall Street trader.
When studying the local history of Earth, or even a small part of it, it is necessary to use the full toolbox of the scientific method. By gazing into space, we can look back in time and see what was happening in galaxies billions of years ago, but we cannot train our telescope on the ancient Earth. Geologists and astronomers have pieced together the history of our planet through the cunning application of all aspects of the scientific method, and it is a field of study that I loved researching for this book. There have been many disagreements among geologists as they pieced together the history of our planet, from how the old Earth might be to whether the continents move or not. These arguments led to new data being collected, and we now have a very good history of our planet. With this short detour over, I return to the history of Earth.
The planet on which we live, with its continents, oceans and diverse forms of life, has not always been thus. At various times in its past, the Earth has had a surface of molten rock, has been covered in a thick layer of ice, has been much hotter than it is today, and much colder. It has been battered by meteoroids, asteroids and space rocks and has even collided with a planet that was about the size of Mars. Our lives are too short to experience more than a tiny fraction of a geological epoch, and apart from the occasional earthquake and volcanic eruption, the geology of our planet appears stable and calm to us, which can be a source of comfort given the turbulence of human existence. But geological stability on the timescale of our lives is an illusion. Our planet is dynamic and is always changing, but the rate of change is slow compared to the three score years and ten of the average human life. Yet each year my hometown of Oxford moves about an inch further away from one of the places where I work, Yellowstone National Park, as the Atlantic Ocean grows wider due to plate tectonics, the slow movement of the great slabs of rock that form the surface of the Earth. Similarly, the tall mountains of Papua New Guinea, where I wish I worked, get taller with each passing year, while the Pacific Ocean shrinks.