How long have plants looked like plants? How long have they been multicellular and, you know, plantish, with different cell types, branching, and an upright structure? Until now, that had been very unclear, but we just got a huge boost in our knowledge.
A once-in-a-generation find (and I don’t think I’m exaggerating) is reported in the February 24 issue of Nature Ecology & Evolution: the oldest fossil of a green plant ever discovered! It is not only 200 million years older than any other example, but it is far more complete and unambiguous.
Qing Tang and Shuhai Xiao from the geosciences department at Virginia Tech made the discovery in the Nanfen Formation in northern China, known to be just about a billion years old, and they have named it Proterocladus antiquus.
Meet the oldest plant we have ever seen:
Here’s the location of this find:
I’ll try to put this discovery into perspective without detailing every controversial fossil and the huge range of opinions on each one. I’ll start with some reasonably common ground: One of the oldest known organisms from the fossil record thought by most (but not all!) to be a eukaryote is this piece of work from about 1.3 billion years ago:
Plants and animals are eukaryotes. Unlike prokaryotes (bacteria, basically), we eukaryotes have cells that contain organelles, like mitochondria to make energy and a nucleus to pack our DNA into. Becoming a eukaryote was the first step, but these are still single-celled organisms. So, how long did it take for multicellular, structured plants to form?
To give you an idea of the wide range of thought in this area, there are claims of seaweed-like multicellular organisms going as far back as 1.7 billion years, but not nearly everyone is on board with that interpretation (they could very well be microbial mat pieces or other organic debris). You’re talking about stuff that looks like this:
Weeellllll….. Multicellular organisms is a pret-ty generous diagnosis of these splotches, wouldn’t you say? But on the other end of the spectrum, some say eukaryotes as an entire class are only 850 million years old.
The evidence for the oldest plausible multicellular “plantish” plant has been very scant, too. Our Virginia Tech researchers point out that the best we’d done so far fossil-wise for green plants was little fragments like this from 750 or 800 million years ago:
The branching suggests it has some plantlike structure, but even that’s not terribly clear. There is also a legit report of red algae in filaments from a billion years ago that is probably multicellular, but it’s a on a different evolutionary avenue from green plants and doesn’t have much structure to it.
That’s why this new billion-year-old find is so spectacular:
So it certainly looks like we had seaweed waving around on the ocean floor a billion years ago, much earlier than we knew, making oxygen and helping to set the stage for us animals (who stumbled onto the scene 600 million years ago or so).
Land plants only appeared 450 million years ago. Did they evolve directly from this kind of seaweed? As you might have guessed, there’s plenty of disagreement about that, too. Xiao sums it up:
“These fossils are related to the ancestors of all the modern land plants we see today. [But] not everyone agrees with us; some scientists think that green plants started in rivers and lakes, and then conquered the ocean and land later.”
Still lots to learn, but discoveries like this are helping us to get there.
A really fun bonus: There is another story out today that is a nifty complement to this.
A lot of attention is paid to the oxygen requirement of animals (we all have to breathe, right?) and how oxygen-producing photosynthesis goes back 3.5 billion years or so.
BUT — for the first time, a true animal has been found that does not breathe! It’s a parasite that infects salmon with what’s called “tapioca disease” and apparently didn’t need to respire anymore in those oxygen-free muscle tissues, and so just dropped it altogether. To be clear, it’s not a bacterium (many of those don’t need oxygen), but rather it’s a multicellular member of the animal kingdom that has sort of backwards-evolved from jellyfish. But again, it’s an animal that doesn’t breathe! The only one known. Well, now you and I know about it, too.
Instead of using oxygen — like you and I do — to accept the electrons left over from its metabolism, it probably secretes lactic acid, ethanol, acetic acid (vinegar), or something like that. But that remains to be determined.
So the cyanobacteria go to all this trouble for billions of years to make oxygen for the animals, and now the animals don’t even want the oxygen anymore. I mean, the nerve. Nature — it’s ALWAYS something. If it’s not one thing it’s another thing…..