Earth’s oldest evidence of life is written in stone – but it’s at risk of disappearing

Today, our planet is teeming with life, but it has not always looked the same. Long before forests reached skyward, animals walked on land, and the rise and fall of dinosaurs, our planet was shaped by a much smaller, more unassuming form of life. And we can still find traces of it today.

These ancient fossils, the earliest visible evidence of life on Earth, are known as microbialites.

Western Australia contains an extraordinary record of microbialites: from the oldest known examples, preserved in rocks almost 3.5 billion years old in the Pilbara, to living examples in the UNESCO World Heritage area of Shark Bay.

Our review of 50 years of microbialite research in Western Australia, published today in the journal Alcheringa, summarises what this archive can tell us about the evolution and resilience of life on Earth.

Despite a fossil record that spans billions of years, microbialites are surprisingly fragile. Fossil sites remain vulnerable to over-collection and degradation, while living microbialites are facing growing pressures.

At sites such as Lake Clifton and Shark Bay, some events may have already caused irreparable damage. One such example was in May 2024, when dozens of aurora chasers trampled 2,000-year-old thrombolites in a restricted area at Lake Clifton.

Earth’s oldest evidence of life

Microbialites are mounded structures that come in many shapes and sizes. They form when communities of microbes either precipitate minerals, or trap and bind sediment.

Types of microbialites can be characterised by their internal structure. Stromatolites are the best known, and have distinctive layers. Thrombolites, by contrast, have a clotted texture.

The microbialite record can tell us a great deal about life on Earth. It gives us clues about where some of the earliest life lived, where we might look for life beyond Earth, and how our atmosphere became oxygen rich, paving the way for more complex life to follow.

Modern sites are particularly important because they help us better understand processes that formed microbialites in the ancient rock record. Living microbialites from Shark Bay have even been described as a “Rosetta Stone” for understanding their fossil counterparts.

Microbialites also preserve evidence of how life responded to environmental upheaval in the past. Western Australia’s microbialite record spans at least one, and potentially two, of Earth’s five major mass extinctions.

This deep-time record suggests microbialites may act as early indicators of ecological stress. Evidence suggests that the sudden increase of microbialites often preceded or coincided with major ecological disruption and mass extinction in the past.

Yet our review highlights several significant knowledge gaps.

Scientists are still debating how to distinguish structures built by life from those produced by non-biological processes. We also cannot always say with certainty what environments ancient microbialites formed in.

There is further uncertainty about what controls the shape and structure (morphology) of microbialites. We also don’t fully know how closely modern examples reflect fossil forms.

Why the internal structure of thrombolites is clotted rather than layered, as in stromatolites, remains a conundrum. So does how far back they extend in the geological record. Western Australia may contain some of the oldest known thrombolites, but these examples have not yet been documented in detail.

In short, Earth’s oldest biological record is not a finished story, although the gaps are slowly being filled. Preserving the evidence, both living and fossil, is essential if future scientists are to answer questions we don’t have answers for yet, or perhaps even to ask questions we have not yet thought to ask.

An ancient archive at risk

Despite their geological longevity and seemingly unchanging nature, microbialites are surprisingly fragile. Their rock-like appearance can make this difficult to appreciate.

Living microbialites can be highly sensitive to environmental disturbance. Their extremely slow growth rates mean physical damage can take decades or centuries to repair, if at all.

Many modern microbialite sites face growing pressures from changes in water quality, climate change and increasing visitation.

Fossil microbialites are also vulnerable. Across Western Australia, tourism, inappropriate collecting and even scientific sampling can damage or diminish these irreplaceable sites. As geological features, their protection falls under geoheritage.

Yet geoheritage remains poorly recognised and under resourced in Australia at both the federal and state levels. The 2021 Australian State of the Environment report concluded that “the overall outlook for geoheritage is poor” due to the lack of national frameworks, focus and resourcing for this area of heritage. Unfortunately, little has changed.

Today, we face an unprecedented and accelerating loss of biodiversity. The microbialite archive offers a deep-time perspective on how ecosystems respond to environmental change, ecological disruption and changing conditions. How far these insights can inform our understanding of the challenges facing life today remains an open question.

Just as important is whether the archives themselves, both living and fossil, will remain intact and accessible for future generations to investigate not only the questions we are asking today, but those we have yet to conceive.