I get a lot of questions about how the world works being a geoscientist and all. I teach students about what we know about our planet on a daily basis and although we don’t know anywhere close to everything, we have come a long way. That is what makes geoscience such a fascinating and dynamic discipline: we have a strong foundation with a multitude of outstanding questions and problems to solve. These questions vary from the very broad (how exactly did the Moon form?) to the very specific (how exactly does barium partition into sanidine crystals?) Yet, we have that foundation that we can all build upon (and even work to refine).
So, I thought I’d briefly list some of what I consider to be the “fundamental truths” of geoscience. This does not mean they will never change — but based on the knowledge we have today, I would be very surprised if we find out something dramatically different. That is really how science works: collect data to support or refute a hypothesis > build a theory from those results > test that theory over and over in different ways > reinforce the theory or build a new one > start testing again.
Let’s take a look!
- The Earth is old … very old. 4.56 billion years old, in fact: Over the last 500 years, what we thought the age of the Earth might be has changed from ~4000 years to over 1 million times that! Where do we get this age? From looking at different elements that decay over time at a constant rate, found in minerals and meteorites. The oldest crystals on Earth (the plucky zircon) from Jack Hills in Australia top out at 4.4 billion years. Primitive carbonaceous chondrite meteorites, thought to be parts of the original nebula that formed the solar system, come in at ~4.56 billion.
- Geologic processes can be gradual … and catastrophic: One of the most important books in the history of geosciences was Lyell’s Principles of Geology. This text laid out the idea that geologic processes can be gradual, so that layers of rock are constructed over long periods and then potentially disrupted by more recent events. It was built on the notion that we can see geologic processes happening all around us, so invoking some unseen event to form a sequence of rocks is not permissible. This was in response to the notion that sediments were all laid down by the Biblical flood. Today, we know that many geologic processes are gradual, so mountain ranges take millions of years to wear down. However, we also know that some events can be catastrophic, such as a giant impact or massive volcanic eruption. Trying to understand what type of process, gradual or catastrophic, is a core piece of geologic inquiry.
- Evolution is real: Darwin was a geologist. Well, he was a lot of things, but he was geologist when it came to thinking about the timescales of various processes. The evidence he collected about evolution pointed towards longterm — longer than the human lifespan — processes that caused one species to become another due to forces in their environment. Today, we find evidence of evolution in the geologic record (fossils) and in the modern record (divergence of species). Evolution can be complicated and get disrupted by catastrophic events, but it is how life has changed on our planet.
- Extinctions happen: A key piece of the evolution story are extinctions. Over Earth’s history, countless species have gone extinct — the place where where one lineage ends (and potentially another begins). Some organisms end up being a dead end while others flourish, based on environmental forces. However, occasionally we have mass extinction events, where lots of organisms die out at the same time. We’ve had 5 major extinction events on Earth starting as far back as the Cambrian, 540 million years ago, up to the end of the age of dinosaurs, 66 million years ago. We will likely see more mass extinctions in the future and nailing down their causes continues to be a major research area in the geosciences.
- Current climate change is driven by human activity: Speaking of extinctions, the climate is changing on Earth! Things are getting hotter and it is pretty clearly caused by the massive addition of carbon dioxide into the atmosphere. It isn’t the volcanoes or the sun doing it. No, it is us pesky humans taking carbon buried in the ground in the form of oil, natural gas and coal, and burning it to form carbon dioxide. That gas gets into the atmosphere and forms a warming blanket for the surface — yes, the Greenhouse Effect — and we’re seeing the results of that anthropogenic geologic event. Now, the question is whether we want to bother to do anything about it or let another extinction reset the planet.
- Plate tectonics is happening: Every discipline seeks a “unifying theory” that can bring together a wide variety of phenomena. In geosciences, we have plate tectonics. The Earth’s crust is divided into dozens of plates, some oceanic, some continental, which move on a plastic mantle underneath. They interact to form mountains, faults, volcanoes, ocean basins and more. We can see it happening by measuring the motion of the land surface via GPS and we can read its past record in the rocks, where we can match features across what are now giant oceans. Earth appears to be unique in the solar system with this kind of rock-based plate tectonics (some moons like Europa have ice tectonics), so we have to wonder why Earth is so geologically active compared to Mars or Venus. More great questions to ponder!
- Earthquakes and volcanoes on Earth are not triggered by other planets: These last two are maybe a little bit smaller points but ones I get a lot. No, we don’t need to look to space to determine why earthquakes happen and volcanoes erupt. Earth’s internal plate tectonic forces are enough to trigger these events and the influence of planetary alignments do not have any discernible impact on when and where earthquakes or eruptions happen. Time and time again, people have looked for these patterns and found nothing — in fact, the evidence points more toward a random distribution of events rather than any patterns. But that won’t stop people from trying to find patterns in the noise.
- Yellowstone is not about to erupt: Finally, no, Yellowstone is not on the verge of an eruption. It just isn’t. There aren’t any signs of this and what we see at Yellowstone are just the signals of a restless caldera doing it’s thing. Even if it was heading towards an eruption, the most likely event would be relatively small, like a new lava dome, rather than the “supereruptions” that the media love to write on and on about whenever a new bit of research is published or another earthquake swarm shakes the area. So, calm on down, folks!
Got any other suggestions? This is a start but by no means the end of some fundamental ideas and processes we’ll discover about the planet.