What Happens When Humans Show Up: On the Ecosystem Beneath Our Feet

The Coral Coast Highway, a renowned road trip, begins in Perth, Australia and stretches along the coastline to Exmouth. Halfway through this scenic journey, a W-shaped configuration of bays separates the highway, marking the westernmost point of Australia: Shark Bay. Designated a UNESCO World Heritage Site, Shark Bay earned its name from British adventurer and naturalist William Dampier, who marveled at the bay's abundance of marine life during his visit in 1699.

However, Dampier overlooked the presence of the oldest life forms on Earth, which have persisted for 3.5 billion years. Upon examining satellite imagery of the area, it becomes apparent that one of the two bays, the rightmost, displays a deeper emerald hue due to its isolation from the ocean by sediment and seagrass, leading to salt accumulation.

Hidden at the southern edge of this hypersaline pool lies Hamelin Pool, home to peculiar dome-shaped structures known as "stromatolites." Though they may not appear as captivating as the sharks, these rocks hold immense significance as ancient survivors and the origin of oxygen, soil, and terrestrial life on our planet. Approximately 750 kilometers northeast of Shark Bay, in the Pilbara Craton region of Western Australia, a series of undulating red hills stand as remnants of a shallow marine environment from around 3.4 billion years ago.

Within these hills, some of the most important records of early life on Earth can be found: extensive fossilized stromatolites, the earliest evidence of microscopic life on our planet. Stromatolites comprise "layered rock" in ancient Greek, denoting the layers of biofilm produced by colonies of microorganisms as they convert sunlight and chemicals into energy, building upward in layers.

For billions of years, these microbial mats were the principal form of life on Earth, representing our earliest terrestrial ancestors. Velvet worms, for instance, have remained remarkably unchanged for over 400 million years, still resembling their Cambrian marine forebears. Approximately 2.1 billion years ago, the "Great Oxidation Event" occurred.

Following the emergence of photosynthesis by marine cyanobacteria, the oxygen produced by these stromatolites eventually saturated the oceans and began diffusing into the Earth's atmosphere, eventually displacing methane as the primary atmospheric gas. While this oxygen-rich environment benefits modern humans, it posed a significant threat to the predominantly anaerobic microbial life at the time, which relied on non-oxygen-based energy sources (similar to the sulfur-based microbes found in deep-sea hydrothermal vents).

This was likely the planet's first mass extinction event. Remarkably, the stromatolites managed to adapt to these new conditions and survive. The decline of methane in the atmosphere, coupled with the formation of the UV-protective ozone layer, led to a cooling Earth and one of its earliest ice ages. Increased oxygen levels triggered the oxidation process, resulting in the reddish hue observed in early pre-soils.

Over a billion years of bacterial activity, life on Earth gradually evolved, shifting the terrestrial landscape in favor of aerobic (oxygen-based) organisms and eventually, complex multicellular life. Human existence can be attributed directly to sedimentary deposits like those found at Hamelin Pool. Over the subsequent billion years, life on Earth continued to develop, with the origins of soil dating back billions of years, although they initially lacked plants or animals and formed under an oxygen-free atmosphere.

Pedogenesis – the study of soil development – considers five primary factors: parent material, climate, topography, biology, and time. While human activity could be added as a sixth factor in the contemporary Anthropocene era, early soils were primarily chemically weathered by water and atmospheric gases. Similarly aged chemically weathered "paleosols" have been discovered on Mars, indicating that similar soil formation processes occur elsewhere in the universe as well.

These ancient deposits are differentiated from true soil due to the absence of a crucial component: organic matter. These pioneering organisms anchored themselves to the barren rocky terrain using roots, marking a revolutionary development in soil formation. The presence of organic matter in modern soils, created by the decomposition of the carbon-rich litter layer above, has been integral to supporting diverse life forms.