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In the Beginning
In the Beginning
Precambrian is the period of the first 4 billion years of this planet.
It is divided into several eons, including the Hadean, Archean, and Proterozoic. It finishes with the Ediacaran Period, lasting for 100 million years, that occurred after 'Snowball Earth'.
After this we move to the Phanerozoic (current) eon, the first period of which is the Cambrian, which is where the soil story starts.
But let's have a look at the goings on for billions of years before that...
Hadean
Hadean
When the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has an atmosphere and a central core, a rocky mantle, and a solid crust. It is that crust, and its interface with air, which is vital to our lives.
Liquid water may have existed between 4.0 and 4.4 billion years ago, very soon after the formation of Earth. Liquid water oceans existed despite the high surface temperature, because at an atmospheric pressure of 27 atmospheres, water remains liquid even at those high temperatures
At first, there was no ‘earth’. Much of the early crust may have glowed red or white, like modern volcanoes. 'Earth' – or soil - arrived much later.
Earth
The name we have given this planet comes from German, about a thousand years ago (tya)
It simply means 'the ground’.
Archaen
Archaen
Signs of life appeared about 3.5 billion years ago. There was an increase in oxygen thought to be a result of the evolution of photosynthetic bacteria, particularly cyanobacteria. These ancient microorganisms are believed to be responsible for the process of oxygenic photosynthesis, where they use sunlight to convert carbon dioxide and water into glucose, releasing oxygen as a byproduct.
The ocean bed sediments changed as a result of the changes in oxygen concentrations in the water, and these sediments subsequently became rocks - but not straight away; the process of turning submarine sediments into rocks requires deep burial. The water provided an environment in which chemical reactions could take place. It was within these early oceans that the fundamental biogeochemical circuitries of carbon, sulphur, nitrogen and phosphorus cycling were established—microbial functions that still underpin all functioning ecosystems on the Earth today. LUCA was most likely a single-celled organism that lived between three and four billion years ago.
Life got going, either from warm little pond, as Darwin suggested, or deep oceans as we now suspect.
Precambrian paleosols
Precambrian paleosols
Precambrian paleosols, or ancient soils, provide valuable insights into all manner of what was going on. They can show Climate and Weathering due to mineral alterations, Atmospheric Composition by the presence of specific minerals or isotopic ratios, Biological Activity, due to the presence of microbial structures, Tectonic and Geological Processes, Landform Evolution through sediments, Cyclical Changes through layers of paleosols and Dating Geological Events by radiometric dating techniques. They also tell us there were no soil structures as we know them today.
Lipid Hypothesis
Lipid Hypothesis
There are several hypotheses regarding the origin of life and the formation of early membranes. The 'lipid world hypothesis' (Lombard, López-García, and Moreira, 2012) is the self-assembly of simple organic molecules, particularly lipids, in water. Lipids like fatty acids could have been produced 'before life'. They are molecules that have both water-attracting and water-repelling (phobic) parts. This phobic effect would make them form aggregates. As more lipids joined the aggregates, they could have formed simple bilayer structures - the basic building blocks of cell membranes. These could have incorporated other molecules, eventually developing the ability to maintain internal chemistry distinct from the outside.
Biofilm
Biofilm
There were the beginnings of a biofilm on rocks and sediment surfaces. Stromatolites are trace fossils of biofilm activity dating back over 3 billion years. They are a layered trace fossil formed by the accretionary behaviour of biofilms populated by photosynthetic microorganisms such as cyanobacteria, as well as others like sulphate-reducing bacteria and Pseudomonadota . Some stromatolite biofilms produce oxygen (those populated by cyanobacteria) while others do not. The extension of these biofilms across land surfaces may well play a vital role in soil formation later.
Stromalite
Two billion years ago, we could see for the first time how biological processes could affect the geological make-up of the surface of the planet. Huge deposits of banded iron formations, which provide the majority of our iron, were the product of biological process - especially photosynthesis. Dead plankton was pressurised and compacted into a substance we know as graphite. This will not be the only time we see living matter ending up as carbon. Just as we use this substance today for lubricating locks and cogs, then graphite lubricated the movement of crustal tectonic plates of rocks. It allowed the formation of mountain ranges, as the rocks could move more easily over each other. (Parnell 2021)
The first bacteria were identified on Dec 26 1676, by Antoni van Leeuwenhoek. He liked using his microscope to look in all sorts of fluids. He drew the first bacterium, now identified as Azotobacter. Bacteria can manage to live in all sorts of circumstances.
Spiral bacteria using lens of Leeuwenhoek
Bacteria
Bacteria
In July 2018, scientists reported that the earliest life on land may have been sulphate-reducing bacteria over 3bya "Calcifying microbial mats in hypersaline environments are important model systems for the study of the earliest ecosystems on Earth that started to appear more than three billion years ago and have been preserved in the fossil record as laminated lithified structures known as stromatolites. " (Spring 2019).
Single-celled organisms called Cyanobacteria (below) appeared around 2-2.5bya. They are the first major wave of bacteria on the planet. We have a lot to thank these organisms. Early photosynthesis was carried out without oxygen, Instead, the early bacteria used hydrogen, sulphides and amino acids to transfer electrons and thus get energy.
They are called ‘prokaryotic’, the name derived from Greek, meaning before the kernel or nut; this is before the nucleus. They come in several shapes and measure between 0.5-20 micrometres. They were one of the first living cells to evolve and have spread to inhabit a variety of different habitats. Over the years bacteria called chemolithotrophs can be found in hydrothermal and volcanic vents. They are everywhere in soils, moving along the walls of the pores.
Bacteria reproduce via binary fission – replicating identical forms. Yet they are known for their ability to change. How do they do it? Their DNA gets transferred in various ways. In transformation, the recipient bacterium takes up extracellular donor DNA. In transduction, donor DNA packaged in a bacteriophage infects the recipient bacterium. In conjugation, the donor bacterium transfers DNA to the recipient by mating.
Cyanobacteria use light, water, and carbon dioxide to produce oxygen and biomass. Once you have oxygen, you have a whole new biosphere.
Cyanobacteria
Cyanobacteria
Cyanobacterial evolution started about 2000 Mya, revealing an already-diverse biota of blue-greens. Later they evolved pigments like chlorophyl which helped them photosynthesise – ie trap sun’s rays and turn into a form of energy which they could use later. As we will see, these became enclosed in many plants as time goes on, performing a variety of important functions. Cyanobacteria remained the principal primary producers from 2500–500 Mya,
By producing and releasing oxygen as a by-product of photosynthesis, cyanobacteria are thought to have converted the early oxygen-poor atmosphere, and created the ‘Great Oxidation Event’. While it may have fed other organism, it may also have been poison to others. The oxygen released led to the "rusting of the Earth". Any ferrous (FeII) iron in minerals and in aqueous solution was oxidised mainly to the red hematite. This was washed or blown away to cover sand grains. It was only after a lot of oxygen reacted with these minerals that there was enough left to build up in the atmosphere. This changed the composition of the Earth's life forms, being particularly unfavourable to organisms that had previously existed without oxygen – anaerobic ones.
Proteobacter
Proteobacter
Following the rise in atmospheric oxygen produced by cyanobacteria, a new phylum called proteobacteria evolved around 1.5 mya. Today this phylum includes many free-living nitrogen-fixing bacteria, such as Azotobacter, & Beijerinckia, and pathogens like the well known Clostridium.
Back then some bacteria would have fed on organic matter, as there would have been some around, but none has been found in the geological record.
Azotobacter
Azotobacter
Azotobacter is a famous free-living bacterium that ‘fixes’ nitrogen from the air to provide vital nutrients. To this day it is sold as a biofertiliser. This protobacteria probably evolved around 1 bya and must have played an important role much later in the development of soils since then.
Viruses
Viruses
Virus probably co-existed with bacteria from very early days and are the smallest of all the microbes – around 500 million on a pinhead. Basically, they are a bit of D/RNA with a coat, which has markings making the virus unique. Look how uniqueness of the coronavirus was that caused the 2020s pandemic.
Viruses cannot live on their own and exist only to make more viruses. The virus particle attaches to a ‘host’ cell, like a bacterium, before penetrating it and then uses the host cell's machinery to live by.
Soil Virome
Soil Virome
Nobody knows diversity of soil viruses – known as the soil‘virome’. Most believe the majority of viruses in soils infect bacteria. This fits with the idea (and It is only an idea) that soil viruses would have been around when the bacteria were building during this half billion years. As the years have gone on, they have infected many other organisms, including archaea, protists, fungi, and perhaps later nematodes, annelids, arthropods, plants, and burrowing animals. All are likely hosts for soil viruses.
Soil viruses in bacteria have received the most attention, but with an estimated 10,000 bacterial species, our present knowledge regarding diversity of infection scarcely scratches the surface. Viruses infect hosts within the 3 phyla Gammaproteobacteria, Firmicutes, and Actinobacteria.
Viruss are being leached from permafrost Despite being up to 48,000 years old, several of the viruses were able to replicate within amoebas, causing them to burst open and release fresh viral particles.[4] Clearly they can withstand all sorts of conditions soil may go through.
If we could look round at what the Earth looked like a thousand million years ago (1000mya or 1 bya) we would see no sign of soil. There was cyanobacteria, viruses and oxygen.
So lets have a closer look at the next 500 million years..
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