What were the First Organisms that Inhabited the Earth Like?

Simon Doyle

The first organisms that inhabited the Earth were microscopic prokaryotic unicellular beings, known as bacteria, whose age dates back to 3.8 billion years and arose as a result of prebiotic evolution.

These organisms were the only living things that populated the planet for more than 2,000 years. Its discovery in 1683 is due to the Dutchman Anton van Leeuwenhoek, who built the first lens microscope and was able to observe them.

They have always had various sizes and shapes, although the most common bacteria can measure up to 2 micrometers wide by 7 or 8 micrometers long. They are classified into cocci, bacilli and helical forms.

What are single-celled organisms?

Prokaryotic unicellular organisms are known as bacteria, but they are also called monera Y schizophyta.

They are the most abundant living beings on the planet. They have an omnipresent nature; that is, they inhabit any surface or habitat: on the ground, air or water.

They are classified into two large groups: bacteria and archaea..

1- Bacteria

They are prokaryotic microorganisms, because they do not have a cell nucleus and have free DNA in the cytoplasm.

They were the first living beings that were born and inhabited the planet and, from them, the evolution of life and species began.

2- You arches

Like bacteria, these unicellular microorganisms do not have a nucleus or internal membranous organelles..

Although they have a similar morphology to bacteria, they differ from these because they have different genes. In addition, they make up their own kingdom or domain.

There is another group that differs from the previous two, called eukaryotes (eukarya), to which the rest of the living beings belong.

This group of multicellular organisms with more complex life forms includes protists, fungi, animals and plants..

Bacteria history

The oldest bacterial fossils date back 3.8 billion years. From then on they evolved and were the genesis of all living beings that we know today..

Recently it has been discovered that LUCA (Last Universal Common Ancestor, for its acronym in English), the most primitive ancestral bacteria from which life comes, had autonomous life and was composed of only 572 genes, while humans have 30,000 genes.

The first unicellular microorganisms, in the absence of oxygen in the atmosphere, fed on the anaerobic degradation of organic molecules. Its evolution to more complex life forms took about two thousand years

The discovery of these microorganisms, in 1683, is due to the Dutchman Anton van Leeuwenhoek, who built the first lens microscope and was able to observe them.

However, the true scientific study of unicellular bacteria and other microorganisms began in 1859 with Louis Pasteur, who opened the way to microbiology.

Types and forms

Bacteria come in a variety of sizes and shapes. These can measure 2 micrometers wide by 7 or 8 micrometers long. Although the most frequent species measure between 0.5 and 1.5 micrometers (μm).

By their shape, bacteria are classified into three main types:

1- Coconuts

They are spherical in shape and are divided into four types: diplococcus, tetracoccus, streptococcus, and staphylococcus..

2- Bacilli

They are shaped like a stick.

3- Helical shapes

They are divided into vibrio, spirillum and spirochete.


  1. Brown J, Doolittle W (1997). "Archaea and the prokaryote-to-eukaryote transition". Microbiol Mol Biol. Retrieved October 4, 2017 from ncbi.nlm.nih.gov
  2. Two faces of the prokaryote concept. Jan Sapp. Department of Biology, York University, Toronto, 2006. Consulted of scholar.google.co.ve
  3. DeLong E, Pace N (2001). "Environmental diversity of bacteria and archaea". Syst Biol Taken from scholar.google.co.ve
  4. Prokaryota. Consulted of es.wikipedia.org
  5. The ancestor of all living beings was a bacterium with less than 600. Taken from elpais.com
  6. Biography of Anton van Leeuwenhoek. searchbiografias.com

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