The Oldest Plant-Like Fossils Ever

Figuring out the origins of life on Earth is like putting together a huge puzzle, where
all the pieces are buried in a bunch of rock and spread across the entire planet.
Scientists have to rely on tiny structural clues and some good old fashioned guesswork,
even just to decide if a fossilized cell is a bacterium or part of a plant.
And even then, it’s hard to conclusively ID any really old fossils.
But in a paper published this week in the journal PLOS Biology, researchers from the
Swedish Museum of Natural History think that they found 1.6 billion year old red algae.
A lot of ancient fossils contain evidence of prokaryotic life, like bacteria.
Their cells don’t have a nucleus to store DNA.
All plants and animals, including us humans, are eukaryotic, though.
Each of our cells has a nucleus and other specialized parts.
And, at some point, we all shared a common ancestor.
Problem is, it’s hard to know when that first eukaryote popped up on Earth, since
it’s so tough to find and identify the oldest fossils.
A paper published in 2000 identified one species of red algae from 1.2 billion year old fossils
found in arctic Canada, which used to be the oldest eukaryote scientists were pretty sure of.
It also happened to be the oldest complex multicellular organism we knew of, too – one
that seemed to have multiple cell types and a 3D body plan.
And now, these scientists think they’ve found two species of multicellular red algae
in some sedimentary rock from central India that dates back 1.6 billion years.
One of the fossils is made of thin filaments, divided into compartments that the researchers
think are cells.
Because of how big those cells are compared to the cells of other organisms, and some
distinct structures inside those cells, they think it’s eukaryotic – specifically,
a kind of red algae.
It’s hard to tell exactly what intracellular structures you’re looking at just from a
fossil, because scientists don’t know whether the shape and position of those structures
is the same as in a living organism.
But in each of these cells, in basically the same place, there’s something roughly diamond-shaped.
And the scientists think this could be a pyrenoid, a kind of protein in algae chloroplasts that’s
involved in making starch, which lets them store up carbon during photosynthesis.
The second fossil is more of a blob shape.
There are multiple masses of cells with different lobes – which looks like a structure called
a thallus.
Inside these thalli, there are some regions that look like bundles of filaments, called
cell fountains.
They’re common structures in some red and brown algae.
So even though they can’t be completely positive, the researchers have some pretty
good reasons to think that complex multicellular life was going strong 1.6 billion years ago,
way earlier than we thought!
They suggest this could be enough evidence to continue tweaking the timeline of early
life on Earth.
If these multicellular eukaryotes were already around 1.6 billion years ago, it’s possible
that other complex organisms, like animals, may have started appearing millions of years
earlier than we thought.
Lots of other organisms came later in the tree of life.
And that includes our old pals, tardigrades.
They’re adorable little extremophiles that can survive things that would kill most other
life, from freezing temperatures to high doses of radiation.
And scientists have been trying to figure out what’s gives them these biological superpowers.
In a study published this week in Molecular Cell, researchers found a group of proteins
that probably protects them from desiccation, or being dried out.
Different organisms have different anti-desiccation strategies to protect their intracellular
bits.
For instance, some use a sugar called trehalose, or proteins that resist damage from heat,
or antioxidants.
But these researchers found certain genes that were activated to produce tardigrade-specific
intrinsically disordered proteins, or TDPs for short.
Now, when water gets sucked out of a tardigrade’s cells, these TDPs start getting glassy – which,
in chemistry terms, means the proteins link together to form a jumbled, amorphous solid.
There are a couple ideas about how this protects everything inside.
One possibility is that this glass-like structure physically prevents all the other proteins
and junk in a cell from bunching up or unfolding, and it keeps any membranes from fusing together.
Kind of like the whole trapping-Han-in-carbonite thing.
Another hypothesis is that because TDPs typically have strong interactions with water, they
could replace the hydrogen bonds that water normally forms with different cell parts,
which protects against the same kinds of cellular damage.
Even though the researchers don’t know the exact mechanism, they were able to test whether
TDPs can help other biological stuff stay safe after being dried out.
Turns out, they do!
Adding some TDPs to yeast, bacteria, and an enzyme called lactate dehydrogenase kept all
three of these things functioning after being desiccated and rehydrated.
So, not only are we one step closer to revealing tardigrade survival secrets, but maybe we
can borrow some of this knowledge for ourselves.
Not to, like, let us trek through deserts for weeks without water.
Although that would be kinda cool.
But knowing more about how tardigrades stay alive could be useful for things like creating
crops that are more drought-resistant, or helping us preserve and transport medicines
that typically need to be kept moist.
Which is not, like never drinking water again, but still pretty useful in the grand scheme
of things.
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The Oldest Plant-Like Fossils Ever

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