The Wonderful World of Stromatolites

Podcast Transcript

If you measure the success of a lifeform by how long they manage to exist on Earth, then by far the most successful forms of life have been stromatolites.

Stromatolites aren’t the sexiest form of life. They still exist on Earth today, but if you have seen them, you might never have known it.

In addition to having been around a long time, stromatolites are responsible for the entire world that we know today.

Learn more about stromatolites, the oldest form of life on Earth, on this episode of Everything Everywhere Daily.

If you aren’t familiar with what a stromatolite is, I don’t blame you. It isn’t something that comes up in most science classes, and you likely aren’t going to encounter one out in the wider world.

Even if by chance you did come across a stromatolite, you probably wouldn’t know it because they look pretty similar to a rock.

So, what is a stromatolite?

A stromatolite is simply a microbial mat. It is a colony of what is usually cyanobacteria, also known as blue-green algae.

More specifically, they are bacterial mats that secrete a cement-type substance that make them look and feel just like rocks. Slimy rocks. They also could easily be confused with coral depending on where you find them.

There aren’t a whole lot of stromatolites in the world today. Probably the best-known location to see stromatolites would be in Shark Bay in Western Australia. I actually went out of my way to make a trip to Shark Bay just to see the stromatolites back in 2008.

I’m guessing there aren’t a whole lot of people who would go so far out of their way to observe what is the equivalent of a living rock, but then again, I do this podcast.

There are several places all around the world where you can find stromatolites, but you won’t find many of them.

They tend to live in extreme regions with high water salinity or some other geological feature that protects them from predation.

Outside of Australia, the best-known stromatolite formations can be found in the Bahamas and Brazil. There are also some freshwater stromatolites that can be found in Canada, Mexico, Australia, Turkey, and Belize.

The modern-day stromatolites are interesting enough, and I’ll be talking about them more in a bit, but they aren’t really why I’m bothering to do an entire episode about them.

What really makes stromatolites something worth talking about is that they are probably responsible for all life on Earth as we know it today….and I do mean all of it.

If we go back in time throughout the geologic record, we find that animals and plants become simpler. 50 million years ago we had dinosaurs, and before that were basic tetrapods, and before that fish, and then about 500 million years go simple creatures like trilobites start to appear in the fossil record.

The period of time going back about 550 million years is known as the Cambrian Explosion because it is then we suddenly see multicellular life starting to appear.

Multicellular life did exist before this event, but they didn’t necessarily level fossils. There are a few places on Earth, like Mistaken Point in Newfoundland, where you can find pre-Cambrian fossils, but they are very rare. They are rare because they had soft bodies that didn’t readily leave fossils behind.

To leave fossils, as you have at Mistaken Point, you needed a perfect storm of conditions to both preserve the evidence of the creature, and then to find it.

If we go back even further beyond that, we are entering a time when all life on Earth was cellular. Individual cells don’t really leave fossils behind, and even if they did, they’d be near impossible to find.

Yet, we often hear about reachers making pronouncements about life on Earth billions of years ago. How is it possible to know anything about this time period?

One of the big reasons is stromatolites.

Individual cells might not leave fossils behind, but stromatolites, aka living rocks, do leave tell-tale signatures in rock strata.

Stromatolites are the oldest direct evidence we have of life on Earth.
The oldest stromatolites that we have discovered are located in Western Australia, about 1000 kilometers northeast of where the current stromatolites live in Shark Bay, near the town of Marble Bar in the Pilbara region.

These stromatolites have been dated to be 3.5 billion years old. That is pretty impressive considering that the Earth itself is only 4.5 billion years old. There are some highly debated stromatolites from Greenland which might be as old as 3.7 or 3.8 billion years old.

Stromatolites grow very slowly. As they are mostly made up of cyanobacteria, aka blue-green algae, only the top surface of a stromatolite would be alive. Over time, they would deposit a layer of solid material which would cause the stromatolite to grow.

When stromatolites are found in the rock layer, they have a very obvious calling card. If you cut them vertically, they look sort of like onions in that they have many thin layers and they are usually curved. If you cut them horizontally, they will look like rings on a tree.

For billions of years, stromatolites were the dominant life form on Earth. Other than free-floating single-cell life which might have been the ocean, you had stromatolites and not much else.

I should stress, stromatolites are not in and of themselves creatures. A stromatolite is a colony of individual cells, not a multi-cellular organism.
It was a stromatolite world for 2 to 3 billion years, depending on how you define it. This is four to six times longer than the period from the Cambrian Explosions until now.

Now before I mentioned that stromatolites were responsible for all life on Earth.

How did that happen?

It has to do with something called the Great Oxygenation Event.

The very early Earth didn’t have oxygen in its atmosphere. Any oxygen which would have been in the atmosphere would have quickly oxidized rocks or carbon and been taken out. This is why many scientists think that if we ever find a planet outside of our solar system with sufficient oxygen, it might be a sign of life.

The early atmosphere was what was called a reducing atmosphere. It may have consisted of hydrogen, carbon monoxide, carbon dioxide, methane, hydrogen sulfide, ammonia, and other non-oxidizing gasses.

At least some, if not most, ancient stromatolites were made up of cyanobacteria, or blue-green algae, which were probably the first cells on Earth to use photosynthesis for energy.

Photosynthesis uses sunlight and carbon dioxide as inputs and emits oxygen as waste.

Starting about 2.5 billion years ago, the amount of oxygen in the atmosphere started to accumulate.

This was an extremely slow process. At first, oxygen wouldn’t last very long because it would bind with rocks and organic matter like bacteria and stromatolites.

Eventually, however, as all those oxygen sinks began to fill up, the oxygen accumulated in the atmosphere.

This actually was a disaster for much of the life on Earth at the time. Oxygen would have been incredibly toxic to them and it would have caused a massive extinction event.

However, it also allowed for the appearance of microbes that could use oxygen as an energy source. Something which never could have existed before.

This oxygenation event led to a system of cellular energy which allowed for multicellular lifeforms, and eventually……us.

Peak stromatolites occurred about 1.25 billion years ago, after which they began to be replaced by other life forms.

There are a few theories as to why stromatolites began to decline.
One is that other singular cell life forms such as protozoans might have simply out-competed stromatolites and took their place in the ecosystem.

Another theory is that as more complex multi-cellular animals developed, they used stromatolites as food by grazing on them.

Either way, by the time of the Cambrian, stromatolites were only about 20% as plentiful as they were at their peak, at least in the fossil record. The fact that they are still around today is evidence that they never disappeared entirely, and they always found some small niche in the ecosystem where they could thrive.

There is actually quite a bit that we can learn from stromatolites.

Some geologists have studied stromatolites to determine what the length of a day would have been billions of years ago. Because the stromatolites were photosynthetic, they could determine the number of layers in a stromatolite and determine the number of days in a year.

Based on a 2004 paper published by Chinese researchers, they determined that 1 billion years ago there were 516 days in a year, 12.9 months per year, 40 days per month, and 17 hours per day.

One of the biggest interests in stromatolites today comes from the nascent field of astrobiology.

If we should find life outside of Earth, it probably isn’t going to be some fantasy creature with seven legs. It most probably is going to be something more akin to a stromatolite.

By studying stromatolites and other extreme forms of microbial life, we might know what sort of biosignatures to look for on other planets when looking for life.

One of the reasons why this topic resonates with me is because I seriously considered astrobiology and the study of stromatolites as a field to get into years ago.

Instead, I just decided to travel around the world.

At first glance, stromatolites are some of the most boring forms of life on Earth. They literally don’t do anything. Not many people are going to go on safari to observe stromatolites in the wild.

However, if you dig a bit deeper to understand what they are about, you’ll find that they are the key to understanding the Earth’s past, and maybe even the future to finding life on other planets.

Everything Everywhere Daily is an Airwave Media Podcast.

The associate producers are Peter Bennett and Thor Thomsen.

I got a couple of boostagrams recently from Dave Jones. The first is a boost of 2112 sats from my episode on the history of the submarine.

He writes Gary, have you ever ridden on a submarine? It’s been a lifelong dream of mine. I’m oddly fascinated by it.

The answer to that is no. The closest I can come to that is when I visited a German U-boat at the Museum of Science and Industry in Chicago when I was in Boy Scouts. I’ve wracked my brain to think if I’ve ever been in a tourist submarine, and I can’t think of a time when I did.

I did, however, land and was launched from a nuclear aircraft carrier, and that will be the subject of a future episode.

He also sent a 500 sat boost about the recent episode about the Kennewick Man. He writes, Have you ever done an episode on Piltdown man?

I haven’t yet, but that is definitely on the list for future episodes. For those who don’t know what Piltdown Man is, it was a hoax of an ancient human skull that was reportedly discovered in the early 20th century.

Thank you very much for the stats, Dave. Remember, you too can send a boostagram by using a modern podcasting app that can be found at newpodcastapps.com

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