What Are The oldest creatures alive on Earth? ?

Biology, geology and paleontology are concerned with finding creatures deeply rooted in history and probing their secrets in order to explore the stages of existence on Earth.

Much scientific research has concluded that bacteria and microorganisms could be the oldest living organisms on Earth, dating back several million years.

Blue-green algae are among the oldest living organisms that produced oxygen through photosynthesis and lived more than 3.5 billion years ago.

Cyanobacteria: 

a type of bacteria believed to have existed around 2.8 billion years ago and which plays an important role in the formation of the Earth's atmosphere by producing oxygen.

Proterozoic eon: 

during which the original nuclear cell as well as multicellular organisms appeared.

Next comes geological red algae:

 the remains of which have been discovered in rocks approximately 1.6 billion years old, and are among the oldest life forms with multiple cells.

Geological green algae are among the oldest multicellular life forms, and research indicates they appeared around 1.2 billion years ago.

The history of these very ancient organisms is therefore an expression of the depth of the progression and development of life on Earth.

Green algae are a diverse group of photosynthetic organisms, which are found in various environments including freshwater, marine habitats and even in terrestrial habitats like moist soils or on trees.

However, when we talk about "geological green algae", we could be referring to certain species that have left geological traces or are associated with geological processes.

And we can note some specific characteristics of green algae in a geological context like for example:

Stromatolites:

Which are layered structures formed by the growth of cyanobacteria and other microorganisms, including green algae, in shallow water environments.

These structures can be found in fossilized form in ancient rocks, providing evidence of the beginnings of life on Earth.

While cyanobacteria were the primary builders of stromatolites, green algae could have been present in some cases, contributing to the microbial mats that formed these structures.

Then we have the Bioindicators:

Which are species of green algae used as bioindicators to assess water quality in geological studies.

Some types of green algae are more tolerant of pollution or environmental stressors than others.

By studying the presence or absence of particular species in sedimentary records or in modern environments, researchers can infer past environmental conditions or changes in ecosystems over time.

And among the characters there is also the carbonate deposition:

Because certain species of green algae are involved in carbonate deposition processes, contributing to the formation of limestone and other carbonate rocks.

For example, calcareous green algae like Halimeda are known for their role in building carbonate structures in the marine environment.

And over time, these carbonate deposits can lithify into rocks through processes such as compaction and cementation, which are part of the geologic record.

Symbiotic relationships:

Some types of green algae form symbiotic relationships with other organisms, such as fungi, to form lichens.

Lichens can colonize and alter rock surfaces, contributing to physical and chemical weathering processes. While lichens are primarily composed of fungi, green algae play a crucial role in photosynthesis, allowing the lichen to survive in various environments and potentially impacting geological weathering processes.

In summary, although green algae themselves may not be important geological agents compared to some other organisms like cyanobacteria or vascular plants, they nevertheless play a role in various geological processes and can leave traces in the geological archives.

Ultimately, determining the "oldest creatures" can be a complex task due to the challenges associated with preserving fossils, interpreting ancient life forms, and defining what constitutes a "creature."

However, based on current scientific knowledge and fossil evidence, we can list a few contenders for the title of “oldest creatures” such as:

Stromatolites: 

Which are layered structures formed by the growth of microbial communities, primarily cyanobacteria, in shallow water environments. Stromatolites date back approximately 3.5 billion years, making them some of the oldest evidence of life on Earth.

Microfossils: 

Which are small fossils, generally on the order of a millimeter, which require the use of a microscope to be observed.

These are different types of microscopic fossils, such as bacterial-like organisms and single-celled eukaryotes, have been discovered in ancient rocks dating back more than 3.5 billion years. These microorganisms represent some of the earliest forms of life on Earth.

Ediacaran biota :

Or Ediacaran fauna (formerly called Vendian fauna) Consisting of enigmatic fossil leaf- or tube-shaped organisms dating from the Ediacaran:

The Ediacaran period, which lasted from approximately 635 to 541 million years ago, is known for its diversity of enigmatic organisms known as the Ediacaran biota.

These organisms were primarily soft-bodied and are considered among the first complex multicellular organisms in the fossil record.

TheTrilobites:

Which are extinct marine arthropods that lived from the early Cambrian period (about 521 million years ago) to the end of the Permian period (about 252 million years ago). They are among the earliest known arthropods and are one of the most diverse groups of extinct organisms.

Coelacanths:

A group of lobe-finned fishes that first appeared during the Devonian period, about 400 million years ago. While many species of coelacanths became extinct millions of years ago, living species, such as the genus Latimeria, are often called "living fossils" because of their close resemblance to their ancient ancestors.

The Sponges:

Which are simple multicellular animals that have existed for hundreds of millions of years. Fossilized sponge spicules (structural elements) have been found in rocks dating from the Precambrian period, indicating that sponges have been around for at least 600 million years.

These are just a few examples, and the search for the oldest creatures continues as scientists discover new fossils and refine their understanding of the beginnings of life on Earth.