IN THE BEGINNING

“A fertile soil transmits forces. Originally, it was the only material on Earth that could hold water. It therefore became the theater where water, earth, and air could interact, where the earth could express itself in the endless variety of organic life.” William Bryant Logan[1],

Slime

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 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.

[1] Dirt: The Ecstatic Skin of the Earth https://www.goodreads.com/en/book/show/35310

ONE BILLION YEARS AGO (or 1 bya)

If we could look round what it looked like a thousand million years ago (1000my or 1 bya) we would see no sign of soil, like we know it today.

The supercontinent Rodinia began to break up around 825mya and continued for almost a 100 million years, brining with it massive volcanic eruptions spewing out volcanic rock called baslt. This is easily weathered, especially round the equator.

With a microscope we could see single celled organisms and other ones which ‘met up with themselves’. Among the single celled ones were bacteria, and were – part of prokaryotes (ie ‘before’ karyotes). The ones which met up became multi-cellular and called eukaryotes or ‘true’ karyotes. These multicellular types could generate new genetic and cell features, making the evolution of more complex organisms possible. And they could now exist because the atmosphere now had oxygen.

These new range of organisms became so successful, that they began to react more with each other. Various useful traits were selected including the development of eyes and protective armour. The creatures developed hard bodies and various means of movement and visibility.

It was a tough half billion years, as the planet froze over half way through – called ‘Snowball Earth’.

Bacteria

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 is the first to draw a sperm.  He also drew the first bacterium, now identified as Azotobacter, in water that had been steeped in pepper overnight

Eukaryotic

Eukaryotic cells are those with internal organs. One is the nucleus: the control centre of the cell, in which the genes are stored in a membrane. Nuclei evolved when one simple cell engulfed another, and the two lived together, more or less amicably – an example of “endosymbiosis”. The other - the mitochondria – was formed when bacteria were engulfed. Mitochondria provide cells with energy and some developed sexual reproduction. Later eukaryotic cells engulfed photosynthetic bacteria – the Stromatolites - to become chloroplasts.

During this half billion years, the eukaryotes divide into three groups: the ancestors of modern plants, fungi and animals split into separate lineages, and evolve separately. The first multicellular life develops around this time. It is unclear exactly how or why this happens, sometimes form colonies consisting of many individuals. They divide into the sponges and everything else including a small group called the placozoa that they may actually be the last common ancestor of all the animals.

The ancestral eukaryote organism is thought to have been an amoeboid creature that relied on anaerobic or microaerophilic, surviving on v little oxygen. The evolution of those internal organelles – nuclei, mitochondria and chloroplasts allowed a more efficient cellular metabolism, which led the way to the evolution of an enormously diverse array of eukaryotic organisms. Some of the early amoeboid eukaryotes developed flagella to enhance their food-gathering abilities and to provide a more efficient mode of propulsion. The flagellates gradually evolved different ways of life, and their structures became modified accordingly. 

Protists are all eukaryotic -- meaning they single-celled organisms and have a cell nucleus that stores their DNA. They are one of the six kingdoms of life. They are the evolutionary bridge between bacteria and multi-celled organisms. Protists are often considered animal-like or plant-like because they behave similarly to multicellular organisms.

Protozoa is another name for animal-like protists. They were a dominant form of life on Earth in this period. While protozoans evolved early and have survived to the present day as unicellular organisms, they have undergone considerable evolutionary change. That many species must have become extinct as others appeared can be deduced from the limited fossil record of protozoans.Protozoa cannot make their own food, but instead must ingest other organisms for energy. Most reproduce asexually through mitosis, which involves the splitting of their cell into two identical copies. Some reproduce through meiosis, which is sexual reproduction. Seven phyla -- subdivisions of a kingdom -- of protists are protozoa.

A fundamental shift in protozoan taxonomy occurred in 1990, when American microbiologist Carl Woese and colleagues revolutionized the world of biology with the three-domain classification system of life. Based on sequences of rRNA (ribosomal RNA), Woese’s classification system revealed three major evolutionary groups of life on Earth. One is eukaryotic and two of which are prokaryotic – bacteria and Archaea. It is generally accepted that the Bacteria) are the most distant genetic group of the three.

Viruses

Virus probably co-existed with bacteria from very early days. Viruses are the smallest of all the microbes – around 500 million on a pinhead. Basically, they are a bit of D/RNA with a coat. That coat has other coatings making the uniqueness of the virus. In recent years we have learned how particular that may be as a coronavirus caused the 2020s pandemic. Viruses cannot live on their own – unlike bacteria which manage to live in all sorts of circumstances. Viruses only exist to make more viruses. The virus particle attaches to a cell, like bacteria, called a ‘host’ cell, before penetrating it. The virus then uses the host cell's machinery to live by.

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.[1] Clearly they can withstand all sorts of conditions soil may go through.

Fungi

[1] https://www.livescience.com/zombie-viruses-permafrost-siberia