Initially, it was believed that the first cellular life forms were anaerobic heterotrophs because they were thought to have fed on organic molecules present in the water where the cells originated. However, there are extremely low concentrations or no molecular oxygen as water molecules split through ultraviolet lights. With these results, it is evident that the earliest evolution must have taken place during these conditions. Scientists believe that the first cell originated when it took organic molecules from the hydrosphere instead of producing them from carbon dioxide.
It is also believed that prokaryotes were the earliest organisms found on Earth, having evolved alone for over 1.5 billion years. These organisms are found in any place where life exists. They can thrive in cold, hot, salty, alkaline, or acidic places. Prokaryotic organisms are different from eukaryotic cells in the following ways. First, they are small besides lacking membrane-bound organelles. Most of them also have cell walls. However, their structure and composition are different from those found in fungi, plants, and Protista. They also contain simple genomes that make them possess different genetic replications. Recombination and protein synthesis prokaryotes have a significant impact on the earth because they are responsible for several diseases. Others are used for decomposition processes that form part of the key organisms in life; hence, they sustain chemical cycles. According to existing evidence, two branches of prokaryotic evolution include bacteria and archaea. However, the archaea dwell in life-threatening locations where bacteria make the essential organic and biological features.
Prokaryotes provide metabolic diversity that can be grouped into species that use light energy. These species are also called phototrophs, while those that obtain energy from chemicals in their environment are known as chemotrophs. Others need carbon dioxide and carbonic sources. Those prokaryotes that require one or more organic nutrients to form a carbonic source are heterotrophs. Endosymbiosis is very important in explaining the origin of mitochondria and chloroplasts. According to the observation of Charles Darwin, those organisms that are strong enough to succeed in the game of survival always stand a good chance of passing their genes to the next generation. This underpinning implies that the first eukaryotic cell has a better advantage over others where the mitochondria are moved. Other pieces of literature also reveal that endosymbiosis plays an important role in continuing life on Earth.
Fossil historians posit that eukaryotes are the beginning of life in plants and animals. According to the evidence gathered from micro-fossils, it is believed that life came to Earth about 500 million years after the formation of the planet. As scientists compared the existing molecular sequences of genealogies, they ascertained that the two primary lines of the same descent led to common microbes that included the photosynthetic bacteria and archaea (prokaryotes and eukaryotes that include all higher plants and animals. These events can be found by studying fossil stromatolites. Nonetheless, the eukaryotic family is perceived to have existed longer than the other species. Various researchers have also indicated that the stromatolites are not the oldest fossils on Earth. Besides, different fossil records have shown evidence of single-celled planktonic eukaryotes. Some of them date back to 1.7 billion years.
Furthermore, fossil records were important in determining the most recent estimated time when the eukaryotes were abundant. This situation implies that they existed even before they turned into fossils. Nevertheless, it is important to note that the stromatolites provide proof of the prokaryotic life that underpins the existence of sustainable sources of energy in the biosphere.