The Ediacara

Before modern plants and animals, there were one-celled bacteria and eukaryotes. But was there anything in between? For a long time, people did not think so.


Enter the Ediacara

The Ediacara (also called Vendian biota) were ancient multicellular life forms that flourished for a "brief" 70 million years, and then disappeared. They were the first life forms to have distinctive cell types. They ranged in size from a few millimeters to more than a meter in diameter. They had a wide variety of body shapes, but did not have features such a mouth or internal organs. We do not know what they lived on, but speculate that they might have been filter feeders living on microorganisms, or they might have absorbed organic molecules from the water.

What was the world like in the time of the Ediacara?

At the time of the Ediacara, the world was dominated by a supercontinent, Pannotia. The rock record from that time is not very complete, so we do not know exactly what Pannotia looked like. Here is one idea of how the continents were arranged.

Pannotia

Pannotia had three parts, Congo, Proto-Laurasia, and Proto-Gondwana.

Most of Pannotia was located in the southern hemisphere. Over time the continents drifted towards the South Pole. This may have caused glaciers to build up on the polar continents and triggered the Gaskiers glaciation that ended the Ediacaran era.

Pannotia was surrounded by a super sized ocean, the Panafrican Ocean. The Panafrican Ocean was teaming with life, but Pannotia was sterile and lifeless. Life forms that could live on land had not yet evolved.

The Ediacara arose after the end of a period of world-wide glaciation, called the Marinoan glaciation. It ended with another great period of glaciation, called the Gaskiers glaciation

What Did the Ediacara Look Like?

The Ediacara life forms do not look like the plants and animals that arose in the succeeding Cambrian era. We do not know if the Ediacara were the direct ancestors of the Cambrian life forms, or a side branch of evolution that eventually died out. Other animals that lived during this time were sponges and probably tubeworms.

The Ediacara were very successful during their time on earth. Their fossils have been found in

• Namibia
• Charnwood Forest, England
• Ediacaran Hills, South Australia
• Mistaken Point, Nova Scotia

This picture shows an artist's idea of what Ediacara looked like in their natural habitat.

This Youtube video show Ediacara fossils. 

Here is a video of two guys looking at Ediacara fossils at Mistaken Point, Newfoundland. They are wearing paper shoes to protect the rocks. This area is now a protected World Ecological Reserve. 

For more about the Ediacara, go to http://en.wikipedia.org/wiki/Ediacara_biota

What are Cyanobacteria?

Cyanobacteria are bacteria that a capable of photosynthesis. They are are also called blue-green algae, but this name is misleading, since they are not true algae, but bacteria. The name "cyano" means blue, and refers to their blue-green color. Cyanobacteria are one of the most successful life forms that has ever existed on earth.


Small is beautiful


Cyanobacteria are a very ancient form of life, and existed more than 2.8 billion years ago. They are responsible for the modern world that we know today. In the early earth's atmosphere, carbon dioxide levels were 10-100 times higher than they are today, while oxygen levels were much lower than today. As cyanobacteria grew abundant, they reduced the amount of carbon dioxide in the atmosphere, and increased the amount of oxygen.


Other organisms that could not tolerate the presence of oxygen became extinct, or were confined to restricted ecological niches. For example, the bacteria that causes tetanus, Clostridium tetani, is anaerobic and can only survive in deep wounds where there is no oxygen.


Some forms of cyanobacteria can change color according to the light. In red light they produce more phycocyanin, and in green light, they produce more phycoerythrin. Thus, they appear green in red light, and red in green light. This helps them get the most energy from the available light.


What do cyanobacteria look like?


Cyanobacteria clump together in colonies of various shapes. Some form filaments, others form sheets, clumps or globes. Here are some pictures of cyanobacteria.

Stromoliths

Modern Stromoliths

Stromatoliths are large clumps of cyanobacteria. 

Stromatoliths are among the oldest fossils, and still exist today in Australia.  

Cyanobacteria shapeshifters

Cyanobacteria change form as environmental conditions change. 

• The normal photosynthetic cells are called vegetative cells.
• When conditions are unfavorable, cyanobacteria survive as spores,  that are resistant to harsh conditions.
• When oxygen levels are low, some types of cyanobacteria can form heterocysts, which can turn nitrogen gas into ammonia, nitrites or nitrates. Heterocysts have thick walls which contain the nitrogen reducing enzymes.
• Cyanobacteria can form mobile filiaments called hormogonia, that can travel and form new colonies. The cyanobacteria in the hormogonia are thinner than vegetative cyanobacteria.

Where are cyanobacteria located?

Just about everywhere! Cyanobacteria live in the ocean. They also live in fresh water ponds, lakes, streams and rivers. They live in damp soil, and in deserts after a rain.  They even live in Antarctica, and in glaciers, forming "green snow" in the spring. 

One of their most unusual habitats is the  fur of sloths in South America.  Cyanobacteria form a symbiotic relationship with fungi to form lichens. Lichens are able to survive on rocks, and are among the first inhabitants of new land.  

Descendants of cyanobacteria may also be living in every green leaf on the planet. 

It is thought that the chloroplasts in all green plants and red algae were originally cyanobacteria that were engulfed by other microoganisms.  This symbiotic relationship proved beneficial to both the cyanobacteria and the hosts, producing the green planet that we enjoy today.

What are acritarchs?

Acritarchs are microscopic fossils of any kind. They can be archaea, bacteria, or eukaryotes. They can be algae or even egg cases of small metazoa. The biggest acritarchs are about one millimeter in diameter. Acritarchs are a general name for these types of fossils when they cannot be more accurately classified. Once a more accurate classification is made, the organism is removed from the acritarch class.

The first acritarchs are found in the later Paleoprotozoic era. They are simple organisms, and are not very abundant. In the Mesoprotozoic era, acritarchs are more abundant and appear to be definite eukaryotes. They have ellipical shapes, processes, and appear in multicellular colonies.

Acritarchs from the Neoprotozoic era have a great variety of shapes and processes. Some look like modern fungi and algae. Many also had tiny spines. Some people think that the spines were for protection against early predators or grazers who fed on the acritarchs. Here are some pictures of acritarchs.