Soil's Origin Story (And What Gardeners Can Learn From It)

Soils had to come from somewhere originally, but have you thought about how they could have even formed at all?

Afterall, the Earth did not have any soil at one point, and now somehow it does.

Here we'll look at some of the earliest soils on Earth and delve into how exactly they formed, as well as the ways that soils have changed over time.

Not only are Earth's early soils fascinating in their own right, but for regenerative gardeners focused on building our own soils and reducing garden inputs, it's invaluable to learn what we can about the soil formation process.

This will give us important insight which will inform our decisons in the garden, and guide us towards replicating nature's soil-building processes (at a much faster rate).

Where?

Terrestrial Ecosystems Worldwide

There's not a whole lot of intact continental crust remaining from all the way back in the times of the earliest terrestrial microbes. Most of it was recycled by plate techtonics, so evidence of early soil formation is concentrated in 2 places where those early plates are still intact:

• Kaapvaal Craton (South Africa)
• Pilbara Craton (Western Australia)

Both of these places have had intact plates since sometime in the range of 2.7 - 3.7 billion years ago, which means some of the longest archaelogical histories on Earth had the possibility of preservation in these 2 places specifically.

Both of these places also hold paleosol clusters that indicate early Archean soils formed by microbes. Our first clue!

There's not yet consensus on just exactly how early these could have begun (some estimates as old as 3.5 - 3.7 billion years ago) but there's pretty solid consensus that there were microbially-formed soils by at least by 2.6 - 2.7 Bya in these places (if not much earlier).

Recall that the Earth is an estimated ~4.5 billion years old, so we're talking about soil existing for at least half of the Earth's lifespan. Possibly 3/4 of its lifespan! Much longer than you might expect.

When?

The timescales that we're talking about are so extraordinarily vast that I made this timeline just to help us visualize exactly when early soils started to form on Earth.

Just note that these time ranges are all approximations based on current scientific knowledge and are still hotly debated. New discoveries could always drastically change what we think we know about the early Earth.

How?

Now that we've got our timescale set, let's look at how these early soils actually began to form:

Step #1 - Mineral Weathering

[~4 – 3.5 Billion Years Ago, Onward]

This is our first step along the way to forming soils, and provides many of the critical mineral components necessary for soils to form.

Back before plants and soils, the early Earth spent a couple billion years as a ball of rock with water on it.

There were seas and rivers, with a hydrologic cycle surprisingly similar to today. There was wind. And eventually there was early life in the seas.

Along the way, the rocks and exposed geology of the planet eroded due to wind, rain, rivers, tides, and the freeze-thaw cracking cycles into smaller mineral components:

• Sand
• Silt
• Clay

You may recognize these as the mineral particulates that we still find in soils to this day:

Step #2 - Terrestrial Microbes

[~3.5 Billion Years Ago, Onward]

The first microbes to appear on land were mostly cyanobacteria, along with some heterotrophic bacteria and a few other early anoxygenic types of bacteria which didn't rely on oxygen.

This point about oxygen is important, because the Earth's atmosphere was almost completely devoid of oxygen at this point.

The bacteria formed themselves into mats and biocrusts across Earth's rocky surface, colonizing bare rock and loose minerals alike.

After spreading across rock, many of these early bacteria produced acids capable of eroding mineral surfaces - gaining minerals for themselves in the process and speeding up the weathering of minerals in general.

We refer to these processes as microbial weathering.

Carbon Fixation

Tying It Into Garden Soil-Building

Applying Knowledge of Earth's Early Soils In Your Garden

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