Anyone down there?

Does anything live down there? How far down in the earth does life extend?

You can see where this is going. Our Challenge for this week was:

1. What, if anything, lives deep in the earth? I know moles, earthworms, ants, and gophers live in the earth–but they don’t go very deep. Are there any creatures that live REALLY deep in the earth? If so, what are they like?



I started my quest with a straightforward search:

[ life deep in the Earth ]


I was pleased to find some interesting reports about life deep in the crust of our planet. Astronomy.com and Phys.org reports that there’s life, specifically nematodes, that life about 1 miles (1.6 m) underground in South African mines.

Unidentified nematode (Poikilolaimus sp.) in a biofilm of microorganisms, from under Kopanang gold mine in South Africa. By Gaetan Borgonie/Extreme Life Isyensya, Belgium.

This report is from the Deep Carbon Observatory (DCO), a collaborative network of geologists, chemists, physicists and biologists searching for life deep underground.

That’s great! Not only is there small life way underground, but there’s an entire network of people looking for it.

First question to ask: Who / what is the DCO? It’s easy to find the DCO home page, which describes them as

“…a team of scientists…with the support of the Alfred P. Sloan Foundation [investigating] how the deep carbon cycle drives our world.

The DCO brings together a multidisciplinary group of scientists, including geologists, chemists, physicists, and biologists.

The DCO Science Network, is made up of more than 1200 scientists from 55 countries…”

I’ve heard of the Sloan Foundation. That’s a well-known research support foundation that does large grants to further science throughout the world. They’re credible, and when I check the Sloan site, I see their initial grant to Oxford to start up the DCO. And I see their management team at the Carnegie Institute. (Another well-known research place.)

I clicked through on the link to the original report from DCO and found more data. I didn’t know that they also have a project that has drilled 2.5 kilometers into the seafloor, and found microbes in boreholes more than 5 km (3.1 miles) deep.

In addition to nematodes, two types of microbes—bacteria and archaea—dominate the deeper parts of Earth. There are millions of distinct types of bacteria, most yet to be discovered or characterized, that form a kind of microbial “dark matter.” Deep Life scientists say about 70% of Earth’s bacteria and archaea live in the subsurface.

That’s astounding.

Deep microbes are often very different from their shallower relatives, often with life cycles on near-geologic timescales.

In some cases, they exist on nothing more than rocks. No organic materials input required. They directly digest and get energy from the minerals themselves.

What’s more, the genetic diversity of life below the surface is comparable to or exceeds that above the surface.

Luckily, the DCO page (above) links to their peer-reviewed work. Here’s a sample from that page:

The biomass and biodiversity of the continental subsurface. (2018) Nature Geoscience Magnabosco C, Lin L-H, Dong H, Bomberg M, Ghiorse W, Stan-Lotter H, Pedersen K, Kieft TL, van Heerden E, Onstott TC

Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor. (2015) Science Inagaki F, (et al.)


What this tells me is that indeed, life DOES exist way down deep into the earth, and that it’s remarkable.

One of the terms I picked up as I read through these reports is microbiome–that is, the collection of microscopic bacteria and other organisms that live together in a particular environment. Learned that term led me to do this query:

[ deep underground microbiome ]

which leads to all kinds of articles. In these articles we find that:

* deep earth life holds 15 to 23 Billion tonnes of Carbon, 245 – 385 times the carbon mass of surface-living humans

* that is, up to ~70% of Earth’s bacteria and archaea live underground… not out where we can see it!

* deep underground microbes are very different than surface microbes, living life on near-geologic timescales, in some cases consuming nothing more than energy from digesting rocks,

* the genetic diversity of life below the surface is comparable to or exceeds that above the surface,

* microbial community richness relates to the age of marine sediments where cells are found—suggesting that in older sediments, food energy has declined over time, reducing the microbial community

The absolute limits of life on Earth in terms of temperature, pressure, and energy availability have yet to be found. As we learn more, the records are continually broken.

A frontrunner for Earth’s hottest organism is Geogemma barossii, a single-celled organism living in hydrothermal vents on the seafloor. Living in hydrothermal vents on the seafloor, this microscopic spherical bacteria survives at 121 degrees Celsius (251 Farenheit; that’s 21 degrees above the boiling point of water).

And… the depth?

The record depth at which life has been found below the surface is approximately 5 km (3.1 miles). Meanwhile, the record below the ocean is 10.5 km from the ocean surface at 4000 meters depth below the sea floor. (That’s nearly 11 km (6.8 miles).)

Admittedly, these are only microbes–but they’re amazing and live under extreme conditions (which is why they’re called, collectively, extremophiles , but also, hyperthermophiles for those that like it hot).

Ultimately… I think we’ve found our answer–at least for the moment. Nematodes (multicellular life) can exist down to 2.57 km (1.6 miles) underground, while bacteria can make it to nearly 11 km (6.8 miles).

But I’m sure we’re find more, deeper, probably hotter in the coming years.

Other notes:

SRS Regular Reader found some great content as well. Arthur Weiss found this superb BBC documentary about deep life focusing on nematodes (including the remarkable Monhystrella parvella, which lives at 2.2 miles (3.6km) down. See also the article in Nature (a very well-known scientific journal) about the deep-living nemtodes of South Africa.

SRS RR Jon (the Unknown) found that CBS 60 Minutes had done a segment on this: What lies two miles beneath the Earth’s surface? (It’s a bit painful to watch–you can’t skip through the ads–but it’s got some great visuals.)

Research Lessons

While it wasn’t hard to do this piece of research, there’s certainly a lot of stuff to wade through.

1. Keeping all of the research findings straight takes notetaking. I know that I needed to keep a set of notes (in a handy Google Doc) with just the URL, a word or two about what’s relevant, and whether it was from a reputable source, a peer-reviewed journal, or simply a news site.

2. Pick up specialized terminology as you read. Once again we found that as you read, you should pay attention to the specialized language of the articles you see. That’s how I picked up the term “microbiome,” which led to many excellent articles. (Why did that work so well? Because it’s kind of a technical term that’s used in kind-of-technical articles, which is what I was looking for.)

Excellent job this week.

Search on!


P.S. Sorry about the delay in finishing this SRS answer. It’s the end-of-the-year… what can I say? There’s a lot going on!