This blog is by Amelia Penny, a Research Fellow at the University of St Andrews. Amelia has a PhD in palaeontology from the University of Edinburgh and has spent three years working at the Finnish Museum of Natural History. Her research explores how biodiversity changes at key points in the history of life.
Ecosystem engineers
In the first months of my PhD, a few weeks before Christmas, I found myself crouching with a small group of colleagues on a fossil reef in southern Namibia, examining hundreds of small, pale, stick-like fossils. We were taking an interest in these fossils because they are thought to be the remnants of some of the earliest animals with skeletons strengthened by minerals. Nowadays, many animals build skeletons in this way: humans, snails, corals and sea urchins are just some examples. But 550 million years ago, to build a skeleton like this was revolutionary.
Skeletons provide support and protection, and they’re also prone to sticking around in the environment long after the organism which built them has died. For example, the accumulated skeletons of sea creatures help to give coral reefs their structure, creating a solid framework that can last thousands of years. This is just one of the countless ways in which living things modify their environments and impact on other species, through a process which is sometimes called ecosystem engineering.
Humans – engineering Earth
Humans are important ecosystem engineers. Like those early skeleton-building animals, humans are modifying the world’s environments in new ways, and biodiversity – the variety of life on our planet – is changing as a result. For example, changes in our use of land for farming and building are a leading cause of biodiversity loss. The burning of fossil fuels such as oil, gas and coal is increasing the concentration of carbon dioxide in the atmosphere, which is changing the climate and is likely to become a stronger driver of biodiversity change over coming decades. Humans have also moved species around the world, bringing pets, pests and cultivated species into contact with native species which have never encountered them before. All of these processes are likely to have long-term consequences.
Taking a long view of biodiversity change
Geoscientists have key roles to play in understanding how Earth’s biodiversity and environments can change over timescales of hundreds, thousands or millions of years. In the eighteenth and nineteenth centuries, discoveries of fossil animals such as pterodactyls and giant ground sloths alerted palaeontologists to the fact that species aren’t permanent- that they can evolve and go extinct. In fact, fossils tell us that over the history of life, global biodiversity has gone through repeated intervals of boom and bust. Often these dramatic changes have a profound influence on life on Earth. For example, the Cambrian Explosion, more than 500 million years ago, was a rapid increase in biodiversity when most of the major groups of animals first appeared in the fossil record. The mass extinction at the end of the Cretaceous period, 65 million years ago, wiped out the dinosaurs, and mammals took their place as large land animals. These past extinction events have led scientists to question- could human activities be bringing about yet another revolutionary mass extinction?
How can we understand the impact of human change?
Many of the pressures on biodiversity now have no exact historical precedent, but we can still learn from the past. The development of large databases of fossil discoveries, such as the Paleobiology Database, has given an unprecedented view of how the world’s biodiversity has changed over very long timescales. This has led to the recognition that modern rates of extinction may be much higher than background rates estimated from the fossil record: an alarming sign of the seriousness of modern biodiversity loss.
Geoscientists can also use natural archives such as rock sections, ocean sediments or peat cores to understand how life and environments have changed in the past. It isn’t possible to run experiments for thousands or millions of years, but events that show up in these archives can be treated as natural experiments, recording how biodiversity and environments have changed over the long term- through deep time. These records are treasure troves of information on when, why and how species evolve and go extinct, or succeed in adapting to a changing world.
These archives can also be used to answer other important questions about human impacts on ecosystems. Long-term records contain information on environments and biodiversity change from a time before these human impacts began, and provide an opportunity to investigate when, why, and how much humans have influenced biodiversity patterns. Many people alive today are used to ecosystems that have already been damaged, and so information about pre-human biodiversity can help us to understand what a healthy ecosystem looks like. It can also inspire us to think in more imaginative ways about the possibilities for ecosystem recovery.
Working together to understand long-term biodiversity change
Modern biodiversity change is alarming. However, as a proportion of all the species on Earth, the total number of documented extinctions so far is small. Clearly, all is not lost – but there are still many unanswered questions. Scientists, including geoscientists, need to work together to understand how this biodiversity change will play out, over the relatively short timespans of human generations, but also across much deeper time. Human impacts on the planet may have consequences over very long, geological timescales, and geoscience is helping us to understand what this might mean for life on Earth.