You know what plants and animals are, and you’ve probably heard of bacteria, fungi,
and even protists.
But have you ever heard of archaea?
Just like plants and animals, archaea are a category of organisms.
If you haven’t heard of them, don’t worry-- you’re not alone.
Archaea as we understand them today weren’t categorized until the 1990s and have been
slowly making their way into textbooks since.
That means they may not have been in your biology textbook at all.
And even if they were, you might not have learned about them in much depth.
But archaea should not be written off as the forgotten organisms.
They are, after all, some of the most extreme forms of life on earth, continually being
discovered in places we didn’t know it was possible for life to exist.
They’re also the oldest forms of life on earth.
So old, in fact, that archaea are believed to have been present during the extreme conditions
of early earth.
Despite being so old, archaea were discovered by scientists only a few decades ago.
Their discovery sparked a paradigm shift within science that made us reconsider the tree of
life and the way we categorize organisms.
You may be wondering: “Why did it take us so long to discover archaea?”
Join us as we uncover…
Archaea: The Hidden Domain of Life
Hang on, “hidden domain”?
What’s a domain?
Are we talking about the Deep Web?
No-- we’re talking about taxonomy!
Specifically, this is the science of putting organisms into named groups like plants and
animals.
But on a grander scale, taxonomy is what helps us make sense of the tree of life.
It’s an attempt to trace evolutionary history from the Last Universal Common Ancestor to
every species of life that has existed on earth since.
Which organisms are related to which other organisms, and how?
Which organisms are we related to?
In taxonomy, the domain is the highest rank of classification-- every organism that we
know of is a member of one of three domains.
But this wasn’t always the case.
Until the 1990s, the kingdom held the title of highest rank.
Since the concept of domains took a while to make it into textbooks, this is what you
may have learned in school.
Wait, what?
Why was a higher rank of classification necessary?
Wasn’t every form of life already accounted for by the kingdoms?
Yes and no.
While every form of life had been placed into a Kingdom, they had not all been classified
correctly.
Before the Domains were introduced, scientists believed that all life could be traced to
one of two distinct evolutionary lineages: the prokaryotes (bacteria) and the eukaryotes
(everything else).
But it turned out that some of the microbes that we had classified as bacteria were actually
from a completely different lineage.
While they were still prokaryotes, they were not at all bacteria.
Their existence revealed that there were in fact three evolutionary lineages, not two.
These became the three domains: eukarya, bacteria, and archaea.
The domains highlight the enormous evolutionary differences among organisms, a distinction
that was lacking with the kingdoms.
Okay, I guess that makes sense.
But how did we discover that archaea were from a different lineage?
And who made the decision to introduce domains?
Enter a biologist named Carl Woese.
Back in the 1960s, Woese began an enormous undertaking.
He wanted to create a tree of life based on data rather than relying on morphology.
He used a technique called DNA sequencing to categorize hundreds upon hundreds of organisms
and describe their relationships to one another.
This was a painstaking, time-consuming process, and he spent ten years working in his lab before
he came forward with his research in 1977.
It was this research that revealed to Woese that archaea came from their own distinct
lineage.
He had, completely incidentally, discovered a third form of life.
His process for categorizing organisms was also a scientific breakthrough, and his method
remains a cornerstone of biology to this day.
In 1990, he proposed the three-domain system as we know it.
It sounds like Carl Woese made some really important scientific breakthroughs.
I bet everyone thought he was a genius when he proposed the three domains!
Well, not exactly.
When Woese first announced his discovery, no one took him seriously, and he was largely
ignored for years.
His idea had sparked a scientific revolution, just as Isaac Newton did with his Laws of
Physics and Copernicus did with his idea of heliocentrism.
He was about to cause a major paradigm shift within Science, but nobody was quite ready
to believe him yet.
Many biologists had to face the reality that their favorite groups of organisms were mere
twigs on the tree of life, and the implications this held for the magnitude of their own research.
Because of this, Woese was even met with some vicious backlash.
It wasn’t until the 1990s that his idea finally started to gain traction within the
scientific community.
Wow, that’s not what I expected!
I think I understand why Woese’s work was so important now...
But archaea still seem pretty boring to me.
Didn’t you mention something about them being “extreme”?
Tell me more about that!
Fear not!
Our friends the archaea are way cooler than you might expect.
A large number of archaea are extremophiles, which are microbes that live in extreme environments
where most other forms of life cannot exist.
This includes places like glaciers, acid mine drainage, and deep sea hydrothermal vents.
For almost any extreme environment you can think of, there are extremophiles that live
there.
A few of the coolest kinds are:
thermophiles which live in extremely hot environments,
psychrophiles which live in extremely cold environments,
and radioresistant microbes, which live in radioactive environments.
There are also halophiles, barophiles, acidophiles, alkaliphiles, xerophiles, and endoliths.
And these categories aren’t exclusive!
Many extremophiles live in environments that are extreme in more than one way.
For example, deep sea hydrothermal vents are home to thermo-acido-barophiles.
Wow!
My mind is exploding!
Fasten your seatbelts, it’s about to get cooler-- archaea are responsible for some
pretty awesome natural phenomena.
Thermophilic archaea are behind the vibrant colors of the Grand Prismatic Hot Spring at
Yellowstone National Park.
This hot spring is hottest in the center, and cools as the water spreads out and thins
towards the edges.
This creates a temperature gradient within the spring.
Different species of thermophilic archaea thrive at different temperatures, and cluster
in bands.
This creates a rainbow of archaea within the spring.
Similarly, halophiles are responsible for the colors of the San Francisco Bay Salt Ponds.
These ponds are shallow bodies of saltwater that are used to harvest salt.
As the water evaporates, the salinity of the water increases.
Different species of halophilic archaea thrive at different salinities.
The species best suited to the environment at any given time will take over the pond
and determine its color, providing a spectacular visual measurement of the pond’s salinity.
And these are just two phenomena that we know archaea are responsible for-- who knows what
else is out there waiting to be discovered!
Whoa!
I learned so much about archaea today.
And to think, I didn’t even know what they were seven minutes ago!
I’m gonna go tell all my friends how awesome they are.
Thanks!