Saturday, February 24, 2018

"Plants colonized Earth 100 million years earlier than previously thought". Not.

Who knew!?   According to a recent press release headline, plants apparently came from outer space and landed on Earth... at least if you believe a recent press release from University of Bristol about just published botanical research results by some of their researchers (February 19, 2018).  If you then go on to read the research paper, you realize that the study they cite is really about LAND plants colonizing terrestrial areas, which sometimes are called earth, land, soil... any area above water.   So this story is not about all plants, it is not about all of planet Earth; it is about LAND PLANTS and TERRA FIRMA.  

Screenshot of press release from University of Bristol, by (fair use).

This headline conjures up an image of some green plant aliens with seed and spore bomb landing on planet Earth 100 million years earlier than some unspecificed time.

Let's dig a little deeper in the press release. 
 "A new study on the timescale of plant evolution, led by the University of Bristol, has concluded that the first plants to colonise the Earth originated around 500 million years ago – 100 million years earlier than previously thought. ."  
INCORRECT.  What is a plant? Is a plant just land plants?  If so, then what are green algae?  Again, what the authors mean here are land plants, not all plants.  Land plants are green organisms that we find in terrestrial environments, from tiny mosses to giant Sequoias  (not counting some terrestrial green algae). Some green algae (streptophytes) are more closely related to land plants than to other green algae (chlorophytes, yes, biological reality is complicated).

The ancestors to land plants were ancient green algae from the streptophyte group, and green algae still live mostly in aquatic environments, both in seawater and freshwater. If you agree that we should classify life on Earth in groups that reflect their evolutionary relationships, then organisms from the red algae + green algae + land plants form a solid, good group for classification, simply called the Plants or Plantae (see the evolutionary tree below). 
How plants have evolved... a little simplified, but rather scientifically correct...
by Maulucioni - Own work, CC BY-SA 4.0, Source
However, an alternative explanation to this mistake in this press release is that the writers of this press release still followed the old 5-kingdom classification of life. This system has been shown over and over to not be correct evolutionarily, and therefore has been abandoned by modern researchers and taxonomists. The earlier system included ANIMALS, FUNGI, PLANTS, ALGAE, PROTISTS for the eukaryotes - and the Algae group has been shown to be a messy grab-bag of unrelated groups.      If this is what happened, then it is time for a knowledge update for these scientists and the public - new information is always interesting and fun and fascinating, and science is about progress and increased knowledge and changes based on new data, so there is no excuse to hold on to old hypotheses and systems. 
        Teaching the public about new taxonomic results and changes, including the difference (and similarites) between the closely related fungi and animals, or, explaining that the old groups 'Protists' and 'Algae' are a mish-mash grab bag of unrelated organisms that should not be classified together, is what scientists and journalist should do - it should be part of our job descriptions and job expectations.  There is no need and no excuse to hold on to outdated information if you care about scientific accuracy.  There is also no way we as individuals can keep ourselves updated on all new information that is coming out of science on a daily basis; that is why we turn to experts for fact checking and updates.  Change, corrections, and updates should be welcome in science, and it is part of the scientific process and its progress. 

Then comes,
"For the first four billion years of Earth’s history, our planet’s continents would have been devoid of all life except microbes."  
PROBABLY NOT. Well, it depends on what you consider 'continents' and 'microbes'.  Eukaryotes (living things that are not bacteria or archaea, and not viruses either) are known from at least 1.5 billion years ago, first as single-celled organisms and later as multi-cellular critters and plants (from maybe 800 million years ago, at least).  The Earth is estimated to be 4.6 billion years old, that means there might have been eukaryotes in terrestrial environments even if we haven't found fossils of them yet.  They simply might have been too small, not had shells or hard cell walls or other body parts that fossilize well, or not left many traces after themselves.  There certainly was a lot of non-microbial life on continental shelves and in marine environments before 600 million years ago.
"All of this changed with the origin of land plants from their pond scum relatives, greening the continents and creating habitats that animals would later invade."
PARTIALLY TRUE.  What is pond scum?  That also depends.  It can be green algae (chlorophytes) or cyanobacteria that form a foamy filmy layer on top of stagnant pond water.  Green algae are a group of plants that are closely related to land plants (which are mosses, liverworts, conifers, ferns, and flowering plants, plus a couple of other small groups).  But cyanobacteria are photosynthetic bacteria and have been around for many billions of years. Land plants also had and have a lot of relatives that are not associated with pond scum, for example sea lettuce, stoneworts, spirogyra, and gutweed (all from the two green algal groups, the chorophytes and the charophytes).
    And for the record, there are fossils of animal tracks that are older than the known land plant fossils. There are so few terrestrial fossils that it is really hard to know what happened and when and in which order. The fungi (and symbiotic lichens) also seem forgotten in this press release, since they are also known from the earliest terrestrial environments.  (Fungi are not plants, they are their own branch, closely related to animals, maybe something to be considered by vegetarians.)
"The timing of this episode has previously relied on the oldest fossil plants which are about 420 million years old."
WELL... So, what are the oldest plant fossils?  Again, that depends on your definition of plants.  The oldest land plant fossils are about 420 million years old, but there are possible red algae fossils from 1.6 billion years ago and also from 1.2 billion years ago.  There are plenty of additional algal fossils from more than 500 years ago. So, again, speaking about land plants, versus plants, make a big difference.

      "Our results show the ancestor of land plants was alive in the middle Cambrian Period, which was similar to the age for the first known terrestrial animals.”

CORRECT, BUT...  (note how the land plants finally enter the story).  Ancestors, evolutionary speaking, is not just one organism at one time.  Ancestors and their extinct species and populations are lining up as a string of organismal pearls back into the distant, forgotten past. And if we continue to follow the ancestral lineages back in time for plants, it ends up at the common ancestor of all living things, common to bacteria to humans, to wolves, sea cucumbers and molds, and for magnolias and mosses and moths. The common ancestor for land plants only, that is different, that is the ancestral (and extinct) organism that is the closest ancestor to the now living land plants.

HOW TO FIX?  To fix the problems in this press release would be really easy, and here is my suggestion (new or changed words in red and bold):
 Title: Land Plants colonized Earth 100 million years earlier than previously thought
A new study on the timescale of land plant evolution, led by the University of Bristol, has concluded that the first plants to colonise land originated around 500 million years ago – 100 million years earlier than previously thought. For the first four billion years of Earth’s history, our planet’s terrestrial areas would have been devoid of all life except microbes and other small organisms. All of this changed with the origin of land plants from their aquatic green algae relatives, greening the continents and creating habitats that animals would later invade. The timing of this episode has previously relied on the oldest fossil land plants which are about 420 million years old. New research, published today in the journal Proceedings of the National Academy of Sciences USA, indicates that these events actually occurred a hundred million years earlier, changing perceptions of the evolution of the Earth’s biosphere. Land plants are major contributors to the chemical weathering of continental rocks, a key process in the carbon cycle that regulates Earth’s atmosphere and climate over millions of years.
It would also have been nice if scientific names would have been italicized in the press release, as is custom in biology. (See this previous blog post)

WHY CARE? When science is communicated to the public, it is not only important that it is correct, but also that it is understandable by a broad audience.  Clearly defined words and simplicity is necessary, but it absolutely needs to be correct. Otherwise it turns into botanical fake news that mislead the public and upset scientists.  To assume that people only think about land plants when you use the word 'plants' assumes that the public does not know about green algae in oceans or in lakes, you ignore current scientific data, and it also shows that you as a scientist or journalist do not care about the details that build the real story.

As scientists, we often get frustrated when there are factual inaccuracies in how our research results and scientific facts are portrayed by non-scientists.  In this case though, it was the home institution of the research team that introduced these mistakes and inaccuracies in their own press release, and then, assuming it was of course correct, it was picked up by news media. This is highly unusual.  More often it is a journalist without much scientific knowledge that introduces errors or simplifies too much from a press release that was accurate to begin with.

Sometimes seemingly simple omissions (plants / land plants) and capitalization (Earth / earth) really makes a big difference, as shown in this story. ScienceDaily picked up the story from the press release as is, as did, Sci-News, Astrobiology Magazine. But look at BBC, and Atlas Obscura, and Science Magazine  - they use the wording 'land plants' and have accurate information in their articles that were not direct copies of the press release.  Kudos to them!

Note.  One person at the University of Bristol was contacted before this story was written and published on, and this person declined to reconsider word choices or make suggested corrections in the press release.

It is also important to note that the issues highlighted in this blog post are only present in the press release from University of Bristol, not in the research paper itself, nor in the quotes from the scientists in the press release. So it is the dissemination of the research results that is the problematic issue here, not the research itself.

For more reading on plants and algae, I recommend this recent blogpost:
Are algae plants?  from the In Defense of Plants blog

Research paper:
JL Morris, MN Puttick, J Clark, D Edwards, P Kenrick, S Pressel, CH Wellman, Z Yang, H Schneider and PCJ Donoghue. 2018. Timescale of early land plant evolution. Proceedings of the National Academy of Sciences USA.