There are several theories about how life came to be on earth. Because it is very difficult to test them, there are none that are completely accepted.
The earliest evidence of life on Earth comes from fossilized mats of cyanobacteria called stromatolites, found in Greenland and approximately 3.7 billion years old. However, there is no fully accepted way of how these cyanobacteria arose.
Collage of prokaryotic organisms: archaea, cyanobacteria, gram (+) bacillus, campylobacteria, enterobacteria, diplococcus and spirochete.
Therefore, the first organisms that inhabited the earth were microscopic and arose more than 3.5 billion years ago, as a result of a slow evolution from inert matter.
Although it is not known exactly how life arose, it is known that the atmosphere at that time was very different from today.
Inorganic substances gave way to organic components using the energy of electrical discharges, volcanic activity and solar radiation, in the humid and warm environment of the Earth of the Precambrian period.
The primitive atmosphere continuously produced molecules rich in energy, which were concentrated in what is known as primitive broth, and which progressively formed macromolecules of greater structural complexity.
Organic molecules will evolve into living organisms. But what were the first organisms that inhabited the earth like?
The first organisms that inhabited the Earth
It is considered that the first organisms that inhabited the Earth were primitive prokaryotic cells, since there is sufficient evidence of their existence during the Precambrian.
Findings of ancient microfossils dating back 3.5 billion years show that these organisms took 2 billion years to evolve into more complex forms such as eukaryotic cells.
According to the cell theory, all living beings are composed of at least one cell, which makes the cell the fundamental and functional unit of all living beings that we know today.
Prokaryotes
The most primitive organism is the prokaryotic cell, a type of bacteria that lacked a differentiated nucleus and organelles, but had membranous laminae, ribosomes and a circular chromosome.
These original cells were heterotrophic and fermenting, that is, they obtained their food from their environment, the thick primitive broth.
And since there was no free oxygen, their metabolism was rudimentary, completely anaerobic, and inefficient.
But despite having a simple and primitive structure, prokaryotes were so viable that they still exist, thanks to the plasticity of their physiology, which has allowed them to survive in environments where no other organism survives.
Photosynthetic organisms
Later, about 3,000 million years ago, the first unicellular organisms with photosynthetic capacity appeared that, by releasing oxygen, began to transform the atmosphere.
So some prokaryotic cells began to obtain energy from sunlight, releasing oxygen and other organic compounds into the atmosphere as a waste product, thus initiating photosynthesis.
Although several types of photosynthetic bacteria developed at this stage, cyanobacteria, also known as blue-green algae, stand out as they were capable of processing atmospheric nitrogen and carbon dioxide.
These photosynthetic organisms produced enough oxygen to substantially modify Earth's atmosphere, which in turn forced other aerobic organisms to adapt and develop oxygen-using airways.
There are microbial fossils, known as stromatolites, where heterotrophic and photosynthesizing bacteria were found grouped in colonies.
Eukaryotes
Finally, approximately 1,200 to 1,500 million years ago, living organisms evolved until the first eukaryotic cells appeared.
Eukaryotes were characterized by having a true nucleus, surrounded by a membrane, which thrived and consequently developed current life, thanks to biological evolution.
References
- Ana Gonzalez and Jorge Raisman. (s / f). ORIGIN OF THE EARTH AND LIFE. Hypertexts in the area of biology. Universal Virtual Library. Retrieved October 4, 2017 from: Biblioteca.org.ar
- Carlos Arata and Susana Birabén. (2013). CHAPTER 1: ORIGIN OF THE LIVING. Section I: I live it in its simplest form. Biology 4. Santillana Uruguay Editions. Retrieved October 4, 2017 from: santillana.com.uy
- Aragonese Center of Technologies for Education. CATEDU. (2016). THE ORIGIN OF LIFE. Unit 1: History of the Earth and life. Unit 2: Biological evolution. 4th Biology and Geology. ESPAD Didactic Units. Aragonese e-ducative platform. Department of Education, Culture and Sports of the Government of Aragon. Retrieved October 04, 2017 from: e-ducativa.catedu.es
- Francisco Martínez and Juan Turegano. IN SEARCH OF THE FIRST LIVING BEINGS. DEVELOPMENT OF THE FIRST ORGANISMS. Unit 4: The origin of life and the evolution of species. Topic 1: The origin of life. From prebiotic synthesis to the first organisms: main hypotheses. Sciences for the contemporary world. Didactic resource guide. Canary Islands Agency for Research, Innovation and Information Society of the Government of the Canary Islands (ACIISI). Retrieved October 4, 2017 from: Gobiernodecanarias.org