Ediacaran Biota- is it a thing? ⋆ TheScientificRevelation
Ola! Friends. Welcome for another adventure, another chapter The Ediacaran Biota- is it a thing? on “History of the earth” series. Previously we went through a rather nasty and almost lost every hope for life. However, life lives on. Despite snow-covered earth where miles of thick ice had restricted the penetration of sunlight, life had survived. Hanging around volcanoes and slush of equator some microorganism had lived on to handover their legacy. After the Cryogenian period started the new exciting chapter on earth but it was a little different from the previous one.
The Ediacaran period had a unique element and the same element passed on to the next periods. It had metazoan macroscopic life. But mind you it’s not like life emerged in Ediacaran itself. We have fossil evidence of sponges, metazoan life forms well around 650 million years ago in the middle of the Cryogenian period. Ediacaran had seen a collective bloom of macroscopic life. Organisms that were walking basically crawling on the seafloor. Earliest kind of predator and prey. Differentiation of cells that were doing specific tasks of locomotion, digestion, and many more. After cold long winter earth saw the spring of life. Now the question arises that what different happened at that time which promoted complexities of life.
The Throwback to discoveries
Its year 1868 Newfoundland, Canada. On a brisk cold morning, you are getting ready for work. You are in a hurry because you are running a little late for work and breakfast is waiting for you hotly served. After sitting at the dining table and you open a fresh newspaper to read before you will be lost in the daily tasks of the day. You raised the coffee mug to take a sip and at the same time, you suddenly read an article. This news is about the strange discovery of disc-shaped imprints found in the rocks there. You find it fascinating and went for another news. Well, you or most of the people at that time were unaware of the importance of these fossils.
That was the first time well preserved Ediacaran period fossils have been discovered. In 1872 it was suggested that they might be simple kinds of life. Very primitive but indeed more than microbes. Precambrian fossils were discovered in 1848 in England and in 1908 in Namibia. But they didn’t get much recognition.
Findings from the famous Ediacara hills
Everything changed when in 1946 Reginald Spriggs found fossils of someSpriggsike jellyfish in Ediacara Hills of southern Australia. Again his claims were not accepted because he had found those fossils in rock layers older than 550 million years ago. At that time conventional thought was that complex life formed in the Cambrian period and before it everything was primitive. In 1957 a leaf-like fossil was found in England. It was named Charnia and looked like a fern. It had left intricately detailed markings on rocks which suggested that it was a complex life. In the 1960s again we are at Newfoundland specifically in mistaken point, Avalon Peninsula. In rock layers from 570 to 530 million years of age paleontologists have found thousands of fossils from Precambrian time.
What took so long to accept these life forms?
For a long time scientists and experts believed the Cambrian period was the beginning of complex life. Most of the modern phylum developed at that time along with eyes, distinctive digestive and locomotion system. Ecosystems were active with sharp predators and protected prey. They didn’t pay much attention to life which had no skeleton and only preserved as imprints on rock layers. The orthodox community refused to accept the life before Cambrian. On top of that, these organisms were primitive, unlike anything we have on earth today. They got recognition for being very primitive life but not complex important life that existed before Cambrian.
The idea and most of the early knowledge for this blog post had come from The common decent podcast.
Ediacaran period (635–543 million years ago) is the last period of the Neoproterozoic era. In this same era, the earth had seen a life-shattering global cold spell and the breaking up of the Rodina supercontinent. Before it, we have the Mesoproterozoic era mostly comprises of a very stable time on earth known as the boring billion. However, the modern plate tectonic and the mineral revolution started in this era only. The first period of the Proterozoic eon is the Paleoproterozoic era, oxygen was constantly increasing at this time. The timeline of the earth started with Haden eon followed by archaeon, Proterozoic, and then phanerozoic. The great oxidation event, ocean formation, solid surface on earth formed well before any life.
Here I am trying to tell you that whatever we consider as modern macroscopic life formed and became widespread in the Cambrian period. Earth’s life span is 4.5 billion years and in the last 500 million years ago anything resembling life formed.
The flashback of winter and condition on earth
Before Ediacaran all, we had microbial matt. Colonies of microbes releasing slimy green material were all over the globe. The Cryogenian period had ended with the second-largest Marinoan glaciation. When the ice had covered the whole earth photosynthetic life plunged down rapidly and oxygen levels also dropped down. When Ediacaran started and ice started to clear life made a comeback. Photosynthetic life became widespread and oxygen levels increased. Oxygen level was not as equal to recent time but it was enough for complex life. There were lots of changes going on in the Ediacaran period. Just before the start of this period supercontinent, Rodina had broken apart and supercontinent Pannonia assembled. Some honorable mentions are, the moon was closer to earth so tides were high and frequent and earth days were only 22 hours long.
Why life boomed in Ediacaran only?
Well!!! It is complicated to pinpoint or even weigh one reason above another for the rise of early complex life. However, there are some points to consider.
Before the start of the Ediacaran Period, the earth was in the Cryogenian period that ended 635 million years ago. When the ice retreated and melted land was free to react with the atmosphere. Melting of ice and heavy erosion had released loads of nutrients in the ocean. In the presence of nutrients, photosynthetic organisms bloomed and spread. They had absorbed carbon dioxide and released oxygen. Oxygen levels increased and more oxygen means more energy. Life also diversified in this oxygen-rich atmosphere.
What is so special about the Ediacaran biota?
Ediacaran is a little special. We don’t talk about older eras and periods on such a specific basis. As you go farther back in history you will have bigger periods and eras for things to put. For example, we know boring billion was billion-year-old time fame included in Mesoproterozoic and early Neoproterozoic era but we still can’t pinpoint when plate tectonics started and how it affected life. What new mineral formed at what exact time. Oxidation event happened during many periods and eras but we still don’t know for sure when it started or what minuscule changes happened at that time.
You see it very difficult to separate boundaries between events that happened this far back. Obviously, fossils records are scarce and depend a lot on chance. On top of that, you can’t expect microscopic life to fossilized easily. In almost over 90% of cases, fossils tell us everything about that organism and what kind of environment it grew. We can know what species dominated the environment and what was the ecosystem land or water. What resources were available. We have a very good inventory and knowledge about recent Phanerozoic eon from Cambrian till now. With every recent period, our knowledge is more because obviously, we have better fossils and data to study from.
It is still difficult to get any conclusion from the scarce fossil record of Ediacaran biota. We are still in the learning and discovering phase. Life was soft bodies and different back then. Scientists are not sure what is a plant and what is an animal, so putting them in the kingdom and phylum is a discussion of the future. However, Ediacaran is a little special because full communities of soft bodies macroscopic life were found in different localities. Before it, we have found some specimens of sponges but we have discovered full communities of species in Ediacaran only. It shows that in Ediacaran multicellular life was widespread in the ocean thriving and enjoying.
An important disclaimer about Ediacaran biota
I have given it a separate point to discuss two important points about these life forms. In fits of excitement, we always neglect these points.
The misnomer of explosion
Firstly, When lots of fossils from the Ediacaran period were found all over places some experts have given called it The Avalon explosion in the name of the Avalon Peninsula of Canada. Here I want to say explosion can be a misleading term. We had found these fossils which date back during Ediacaran 635 to 543 million years ago. But, how can we be sure that they found or originated only during Ediacaran? Maybe they were roaming well before Ediacaran. When they died time and place were correct for their fossilized.
This is the case with every fossil. You can’t be very sure that when this species lived and went extinct. Perhaps we will discover older Ediacaran biota-type fossils in the future and it is possible that we can find them in the Cryogenian period.
The misnomer of Ediacaran Biota
Secondly, over and again for all fossils experts and scientists use the Ediacaran biota term. We use it because the most famous fossil group that had modified our view of life was found in Ediacara hills. After that discovery organisms from the Ediacaran period found on other continents too. Now for addressing all the Ediacaran life using Ediacaran biota is a misleading term. We don’t know what any of these organisms are. Are they plants, animals, or some kind of entirely new phylum? Maybe organisms found in Newfoundland or England are entirely different from Ediacaran fossils. If we use Ediacaran biota many people assume that all organisms are similar and related which is not true.
Thirdly, I have mentioned that Ediacaran had seen the rise of the first metazoans, animals that have differentiation of cells for specific tasks. However, these animals didn’t appear till late Ediacaran around the Cambrian boundary. There is some jumble of words. Scientists are differencing between Ediacaran Ediacaran-like life forms and Ediacaran non-Ediacaran life forms. The former ones are bizarre animals, unlike anything that grows today or lived at the earliest time. The later organisms were not very alien-like. They had some similarities to the Cambrian life like spriggina that might be related to trilobites.
What is Ediacaran biota?
To make things clear about the fossils I want to say that all we have gotten imprints of organisms between sandstone layers.
The physical dimension
Firstly, those organisms were soft-bodied. They were cartilaginous creatures means there is no hard part that had survived till now. When an organism died it had buried when the optimum situation and the layer were available. But there is a catch. Because these organisms had no hard part so, their body decayed over time and left only imprints or molds in layers.
Secondly, these Ediacaran organisms are so weird, so different from anything living today that we are unsure of whether they are animals or plants or both. We don’t know which phylum they belong to, some of them do resemble jellyfish and sponges but we are unsure. Those organisms had no distinctive body parts like eyes or mouth or skeleton so we can’t put them in phylum as we are unable to identify them.
Thirdly, we need to remember that the Ediacaran biota we are talking about existed before almost 540 million years ago, a very long time. Since that time earth had been changing. Tectonic plates are constantly moving. Mountains had risen on the place of seas and plains have submerged under the ocean. In this dynamic world, fossils have moved a lot and most got destroyed due to the subduction cycle of tectonic plates. On top of that, animals without skeletons can not be preserved much.
Some notable species
Scientists have found some unique organisms from this time period. Generally, the earliest macroscopic life from this time is known as Rangeomorphs. They were like very thin fern-shaped things. They were not plants because they lived in the twilight zone. Too deep in the ocean where not enough sunlight penetrates for photosynthesis. However, these were not animals either. It is a little complicated.
They do look like plants but they were not plants. They used to grow with the same basic structure repeatedly means every branch or appendage was a miniature form of the whole plant. Just try to imagine like a pine tree and every branch of that tree grow like a mini pine tree. So, instead of branches, you will see mini pine trees growing. Which I have to say will look downright creepy. Nothing we know including animals and plants grows in this way. These fern-like things probably were filter feeder means they used to catch whatever they can out of the water nearby.
Some organisms were equally unique like Tribrachidium which had triliteral symmetry. All animals on earth have bilateral symmetry means if we cut them from the center the two parts will resemble each other. Tribrachidium had 3 similar sides out from its body. Nothing we know grows in this way. These Ediacaran period life forms are so different that we are unsure where they can fit in the tree of life. Some experts think that they are a separate kingdom or entirely separate phylum that went extinct. Perhaps they are stem animal, some ancient lineage which existed long before.
The Ediacaran non- Ediacaran forms
Like I have mentioned above some later Ediacaran life was more close to Cambrian forms. These later species were metazoans, which had separate cells for specific tasks. For instance, we have Haootia Probably the first cnidarians family that includes Jellyfish. Haootia might have muscles for different tasks. Then comes Kimberella which has Bilateral symmetry. It was squishy soft with appendages that it used to drag behind. Have you seen how a cuttlefish move? Just in a similar way, a kimberaella moved on the ocean floor. Another organism with bilateral symmetry is Spriggina which might be the ancestor of trilobites.
How these organisms became extinct?
There are many causes for the extinction of Ediacaran life forms. Two major reasons stood the most.
Breakup of supercontinent
Firstly, the breakup of supercontinent Pannonia. If a supercontinent is breaking apart obviously tectonic movement is involved. Absolutely volcanic eruptions have happened. When continents break apart or come together the first thing that follows is volcanic eruptions. It had surely happened at the end of Ediacaran when Pannonia broke apart. Volcanoes produce gases and smog. When volcanic eruptions happened at the end of Ediacaran carbon dioxide levels must have increased in the atmosphere that led to global warming. Global warming and increased temperature made life in the ocean difficult.
The excess gas clouds had enveloped the sun, blocking sunlight and affected photosynthesis. Every organism depends on the sun’s energy for survival whether it is an animal or a plant. Consequently, Photosynthesis suffered and the food web collapsed. Volcanoes also release sulfur. This sulfur after mixing with rain fell as acid rain. As a result, oceans became acidic. Most animals lived under oceans. The scarcity of oxygen and acidic environment had polluted their habitats. . Subsequently, organisms died out.
The fight for survival
secondly, The Cambrian animals pushed the Ediacaran biota towards extinction. This is a compelling hypothesis. Due to volcanic eruptions and lower oxygen levels, Ediacaran lifeforms were already struggling. The came Cambrian animals well equipped with advanced modern features of predation, eyes, locomotion organs, and other body parts. These animals were beyond advance and well suited. Ediacaran life forms had to compete with Cambrian animals for food and space. On top of that Cambrian animals were ecosystem engineers means they were modifying their niches. They were sharing the space with Ediacaran fauna and modifying it over and over
Now you can think for yourself that Ediacaran’s life didn’t stand a chance. In short, already weaken and primitive Ediacaran organisms died out leaving their niches open for others.
- The resource I want to share is a lecture from the Royal Tyrrel museum of paleontology. The title is The Ediacaran period- Glimpses of earth’s earliest animals. You may watch it, it’s very informative.
- Another brilliant lecture on Ediacaran life by Palaeo cast. Watch it.
- A post on Ediacaran life by The burgess shale, Royal Ontario Museum. There are lots of pictures and the simplest overview of fossils from the Ediacaran period.
- Two well-written research papers on the subject The advent of animals by the proceedings of the national academy of sciences of the USA and Ediacaran- an overview by The science direct.
- An honorable mention about Dickinsonia by PBS Eons. Must watch this video.
We used to think complex life originated in the Cambrian period. Few fossils have changed our view on not only when life started but also on how different and alien-looking life can be. Ediacaran fossils were different from what we were used to calling complex life but nonetheless, they were multicellular creatures. As time will pass we might discover even older fossils and maybe our view on life will totally transform. Our next chapter is the Holy Grail of life. Get ready to explore the diverse radiation of life known as the Cambrian explosion. Stay tuned and Do Revelation.
Originally published at https://www.thescientificrevelation.com on March 15, 2021.