Steven D’Hondt is a geomicrobiologist studying life in marine sediment and rock found deep beneath the seafloor – one of the very few ecosystems not yet pervasively altered by humans. His work explores the fundamental limits to life on Earth. The sparse microbes found entombed in ocean sediment live differently than those found in most other environments on Earth.
On average, they are breathing about 1,000 times slower than bacteria in the world around us. This poses many methodological challenges, and makes us question what it means for something to be ‘alive’. According to conventional wisdom, their activity rates are too slow for them to proliferate by cell division — technically, they should barely be able to maintain cellular repair. So, either these life forms reproduce using just a trace amount of energy, or the oldest among them are more than 100-million years old, which would essentially make them immortal. This conundrum is yet to be fully explained, but Steve suspects that the truth lies somewhere in between.
What’s more, the possibility that life could have persisted under such challenging conditions for 100 million years opens up the possibility that there could be life on other planets in our solar system — for example, beneath the surface of Mars or Europa. It’s estimated that Mars had liquid water, and perhaps surface life, a few billion years ago. That’s only an order of magnitude longer than microbial communities studied by Steve and his colleagues have survived.
Ship and drilling crew (in red), catering staff (green), and scientists and scientific technical staff (other colors) on Integrated Ocean Drilling Program Expedition 329, led by Co-Chief Scientists D'Hondt and Fumio Inagaki, with Expedition Project Manager Carlos Alvarez Zarikian. Photo courtesy of IODP JRSO.
Split cores being sampled onboard the ship. The color-coded flags mark intended sampling locations for specific geological studies. Photo courtesy of IODP JRSO.
Fluorescence microscopy image of a microbe in 13-million-year-old sediment (from IODP Expedition 329 Site U1368). The microbe is the bright green dot at the center. Photo courtesy of JAMSTEC.
Steve is closely involved with the international scientific drilling community, such as the International Ocean Discovery Program. He regularly takes part in drilling and coring expeditions with teams of scientists from around the world in search of sediment samples to study.
Life on these ships can be gruelling. From the most senior scientist to the chef, everyone on board plays a vital part in achieving the scientific mission. When it comes to building expedition teams, getting the right team dynamic is crucial. Steve makes sure he has a mix of senior and junior scientists with a range of knowledge and skills. It’s important to him that he helps early-career researchers get a foot on the ladder.
Steve’s work into the unexplored world is fundamentally collaborative. Research of his kind is expensive, and it can take many years to be approved and carried out. The more he can work with other scientists investigating similar themes, the more it will inform his research, and the more he’ll learn. And that, for Steve, is the ultimate goal.
Steve originally trained in geological and geophysical sciences at Stanford and Princeton Universities. When he joined the faculty of the Graduate School of Oceanography at the University of Rhode Island, he worked in paleoceanography, studying the oceans and marine organisms as they were at the end of the age of dinosaurs. It was then that Steve realized the fossils he was extracting were part of a still-living ecosystem. This breakthrough inspired a move into subsurface biology – the study of living organisms beneath the seafloor.
For his latest piece of research, Steve is proposing a drilling mission in the Atlantic to look at the microbial communities that inhabit sediments from different geological time intervals. As part of this research, he’s hoping to probe the memory these communities may have retained of the oceans in which they were first deposited. In doing so, he’ll explore the potential parallels between thermal warming in the late Paleocene-Eocene – which was caused by a fast influx of a large amount of carbon – and human-caused warming today.
When he’s not seeking to answer mysteries about the history and limits of life on our planet, Steve teaches courses in ocean science at the University of Rhode Island. He uses ResearchGate to keep up to date on his colleagues’ and collaborators’ work, and to track new topics. During the COVID-19 pandemic in particular, Steve has been using ResearchGate to reach out to other researchers for access to their papers so that he can share them with his students. For example, he reached out to large numbers of people sharing work on global ocean change when he put together a graduate seminar on the topic.
