The Quest for Earth’s Oldest Fossils: Clay, Decay, and the Rise of Complex Life

In this Royal Society talk, an Oxford paleobiologist discusses how scientists uncover Earth’s oldest fossils, including microscopic life preserved by clay minerals. He explains the transition from simple bacteria to complex eukaryotes, why macroscopic fossils are rare before 500 million years ago, and how researchers use decay-inhibiting clays to preserve fossil cells. The talk outlines fieldwork in Svalbard and northwest Canada, the link to ancient environmental change, and the potential for similar fossil preservation on Mars. A closing note previews a hands-on activity on how to make a fossil for the audience.

Introduction and Research Focus

The speaker, a palaeontologist from Oxford, centers his work on the world’s oldest, smallest fossils. Unlike many palaeontologists who study dinosaurs or trilobites, he concentrates on tiny remains that are difficult to find but incredibly informative for understanding early life and planetary evolution. The talk places the discovery of complex life in a broader context: are we alone in the universe, and how did Earth come to host the majority of biomass and oxygen today?

The Timing of Complex Life and Why Fossils Are Scarce

Earth is about 4.5 billion years old. For most of its history, macroscopic life did not exist. Fossils we commonly imagine—dinosaurs, trilobites—come from the last 500 million years. The early Earth, however, harbored mostly bacteria and simple life. To trace the rise of complex life, researchers must push beyond well-preserved, bone-bearing fossils into murkier, pre-bone eras, where evidence is sparse but crucial for understanding major transitions in biology and climate.

Fossil Preservation and Soft-bodied Organisms

Most fossils preserve bones or shells made of minerals like calcium carbonate. Soft-bodied organisms, crucial to understanding early ecosystems, decay rapidly unless decay is slowed. This decay problem limits our view of the earliest life, leaving only a handful of robust fossils from 0.75 to 1.6 billion years ago. The presenter emphasizes the need to find markers that can survive long decay processes to illuminate early evolution.

Clay Minerals as Nature’s Decay Inhibitors

A central theme is that certain minerals, especially clays found in particular rocks, can slow decay and preserve delicate fossils. Experiments in the lab show bacteria grow poorly in minerals like clays, slowing their decay. Crucially, rocks rich in these clays have a higher chance of yielding fossils from the distant past. A mineral called berthurine (berthurin?) is highlighted as a clay that can encapsulate and protect fossils, enabling micro-scale preservation visible under a microscope.

Fieldwork and Discoveries

Field work is described in two key locations. In Svalbard, the Arctic, rocks are clay-rich, supporting the search for early fossil cells, including an early algae. In the Northwest Canadian region, reefs built by microbes lie near mudstones rich in clays, offering another promising environment for preserving ancient life. These field expeditions aim to fill gaps in the timeline of early evolution, expanding the known fossil record beyond the last 500 million years.

Mars and the Prospect of Extraterrestrial Life

The talk connects Earth-based methods to planetary exploration. The Mars rover Perseverance landed in Jezero Crater, chosen for minerals including clays. The implication is that similar clay-rich rocks on Mars might preserve ancient life signatures, making Mars a compelling target for studying early life in the universe using planet-wide comparative geology.

On-site Analysis and Prioritizing Fossils

In the field, rock samples are dissolved to extract fossils, a time-consuming but essential process. The team wants to develop field-portable chemistry to rapidly identify rocks likely to yield fossils, mirroring some instruments used by the Mars rover but at a more accessible scale for Earth expeditions. Quick chemistry helps prioritize which rocks to bring back for detailed lab analysis.

Q&A Highlights and Audience Engagement

Audience questions cover a range of topics, from how to infer the color of ancient algae to the timing of the first simple organisms, with explanations about stromatolites and carbon isotope evidence. The speaker explains that color reconstruction is challenging for very old fossils, though recent work in younger fossils has allowed color inferences. He discusses evidence for life less than a billion years after Earth formed and the role of isotopic signatures in identifying ancient metabolic processes. The session also touches the possibility of life on Mars being limited to simple, early forms due to Mars’ early atmospheric loss.

Future Directions

The talk ends on a forward-looking note: more fossils from clay-rich rocks will be sought, both on Earth and, potentially, on Mars. The speaker hints at upcoming discoveries from fieldwork in remote Canada and emphasizes the broader relevance of clay-mediated fossil preservation to understanding Earth’s deep-time biology and the possibility of life beyond Earth.

Closing: A Hands-on Fossil Activity

As a finale, the session transitions to an activity designed for kids in the audience on how to make a fossil, including the use of masks prepared by graduate students. The live stream of the activity is said to be switched off to prevent recording of the session.