What are microbes, and wait, they are found in rocks?

A very (in)famous mathematician, Dr. Ian Malcom, Jurassic Park, once said five very insightful and philosophical words. “Life, uh…finds a way

Dr Ian Malcom in Jurassic Park

While he was referring to breeding dinosaurs, which films have taught us is not a good idea, he was nevertheless correct in a different context. Life very often finds a way to exist in unexpected places and ways, and often that life is microorganisms.

Microorganisms are living things that are so small they can not be seen with human eyes alone. These microscopic living organisms are incredibly diverse and can be found in each of the three domains of life, Bacteria, Archaea, and Eukaryota. They are found nearly everywhere on Earth and are extremely good at adapting to their environment: often found living where nothing else can survive. A subset of microorganisms is known as microbes, this often refers to Bacteria and Archaea. Microbes are so small that between 10-20 thousand individual cells can fit on a single full stop (a period for the Americans out there) at the end of a sentence.

In the course of your everyday life nearly everything you touch will have microbes on or in it. They are in the food you eat, the air you breathe, and on the things you touch. Further microorganisms are a part of you:  they are found on your skin, in your mouth and nearly everywhere else too. These microorganisms are typically very helpful, for example your gut microbiota helps with the digestion of your food. Essentially everything humans come in contact with on Earth will have microbial life present. However, they are found elsewhere on Earth as well. Microbes are experts at finding and living in extreme and/or isolated habitats. So what exactly does all of this have to do with rocks, and why does it matter?

Topsoil is perhaps the best place to start. It grows crops, flowers, and supports life on land. A single spoonful of soil contains at least as many microbes as Earth contains humans. These organisms live off of nutrients found within the soil, and help decompose organic material, like dead leaves. They in turn release nutrients back into the system. As you dig deeper through the soil layers you will observe different horizons, until you hit hard rock. Just because you have hit rock doesn’t mean that life is no longer going to be present. The rock below the soil horizons, known as bedrock, is not in fact completely solid nor is it completely uniform. It has cracks, fractures, and vesicles (small cavities formed by trapped gas bubbles). Additionally, bedrock can be very varied in its composition. These voids, and the bulk rock itself can be colonized by microorganisms. They are able to survive and slowly multiply even though these environments only have small amounts of carbon, water, and other essential nutrients available.

Just like on land, there is essentially “soil” on the bottom of the oceans, known as ocean sediment. Ocean sediments are formed differently from soils though. They are a combination of weathered rock (both oceanic and continental), decayed or decaying oceanic life, and at times mineral precipitates. These sediments overlay hard rock just like soil sits on top of bedrock. Oceanic hard rock, known as the basement, is similarly not a single solid block of homogenous rock. Composed primarily of igneous (solidified magma or lava) and metamorphic (rocks transformed by temperature and pressure) rocks the basement is just as variable as bedrock on land. Like bedrock, the basement is home to microbes who exploit small cracks and voids within the rock to establish themselves and exist. Life exists and persists here thanks to rock-forming minerals and the fluids rich in nutrients that circulate through regions of the basement.

Microorganisms that live in subsurface rock both on land and in the ocean are part of a group known as extremophiles, meaning that they live in environments that are typically hostile to other types of life. Further they are classified as cryptoendolithic, or organisms which live inside rocks. They represent just a small fraction of the diverse types of extremophiles found on Earth. Together microbes from bedrock and the basement make up the “deep biosphere”.

The deep biosphere is currently home to more questions than answers, and right now there is very little way to answer questions such as “Why does it exist?”, or “How did the microbes get there?” However, what we do know is that the deep biosphere ecosystems make up a very important, yet poorly understood, section of the global biosphere. Also, throughout Earth history microbes have acted as tiny builders, they provide a unique biological contribution to Earth’s chemical and mineralogical signature.

This research area is really just starting to gain steam within the broad scientific community and the deep biosphere a very exciting, and wide open field right now. Research is occurring in numerous countries around the world. On land some of the sites being studied are found in Iceland, Oman, Germany, the USA. In the oceans scientists are investigating places off of the coast of California, along the mid-Atlantic ridge, and many many others. It is not easy to access the deep biosphere, and scientific drilling is nearly always required. To find out more about how we get our rock samples, and how we explore the deep biosphere stay tuned for later posts about scientific drilling, and feel free to investigate scientific drilling for yourself. A good place to start is the film called “Looking for Life”. It shows how scientists went out to explore life in a deep coal bed far below the ocean floor.

Written by Rachael Moore.

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