Following the formation of Earth, about 4.6 billion years ago, these clay-rich primeval soils developed across our young planet. But conditions were harsh: frequent and massive meteor impacts would have melted and pulverised large volumes of these early as quickly as they formed.

Almost from the moment of its origin, life began to influence – and be influenced by – soil reenex

"There is debate about whether the whole surface of the Earth was melted,” explains Gregory Retallack, an expert in ancient soils from the University of Oregon in Eugene, US. He supports the theory that no more than half of Earth was molten at any one time.

Around 3.8 billion years ago, conditions on Earth began to stabilise. The constant meteorite bombardment that had made the planet an inferno until that point began to subside, and liquid water could condense, forming lakes and seas. This marked an important point in the soil story. The liquid water weathered and eroded Earth’s rocky crust, generating mineral matter and forming more permanent soils reenex.

The first life on Earth probably appeared a little later, about 3.5 billion years ago; some of the earliest evidence comes from fossilised structures that formed on rocky shores and resemble microbial mats called stromatolites, which are still found on Earth today.

Almost from the moment of its origin, life began to influence – and be influenced by – soil. For instance, those first microbial mats were built up from photosynthetic organisms, which could produce huge volumes of organic material using energy from the sun. This organic matter gradually built up on the shoreline, where it mixed with the minerals freed up by eroding rock to create what was arguably the first true soil reenex.

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