On the Origin of Species (more completely, On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life) published on 24 November 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology.

P and R have the same percentage hence they must bond with each other.

The origin of life on earth a scientific problem which is not yet solved. There are plenty of ideas but few clear facts.

It is generally agreed that all life today evolved by common from a single primitive lifeform. It is not known how this early form came about, but scientists think it was a natural process which took place perhaps 3,900 million years ago. 

So, the correct answer is "3.5 billion years ago".

During the profound changes that have been taking place since the remote past we have lost the direct evidences of origin of life. Due to these changes, the scientists, though skilled were not able to protect the evidence.

Charles Darwin’s five-year voyage in the early 1830s was on H.M.S. Beagle. It has become legendary, as insights gained by the Darwin on his trip to exotic places like Galapagos island greatly influenced his masterwork, the book "On the Origin of Species"

The fossil shapes almost 3.5 billion years ago, identify them as archaea.

The early atmosphere of earth was made of nitrogen and carbon dioxide gases before life began. When the photosynthesizing organisms multiplied then the carbon dioxide was replaced by oxygen. So, the correct option is "reducing primitive atmosphere contributed to the origin of life, and the oxidizing one of today would hinder it".

• Cells are divided into two main classes, initially defined by whether they contain a nucleus. 
• Prokaryotic cells (bacteria) lack a nuclear envelope. 
• Prokaryotic cells are generally smaller and simpler than eukaryotic cells; in addition to the absence of a nucleus, their genomes are less complex and they do not contain cytoplasmic organelles or a cytoskeleton. 
• Phospholipids are the basic components of all present-day biological membranes, including the plasma membranes of both prokaryotic and eukaryotic cells. 
• The key characteristic of the phospholipids that form membranes is that they are amphipathic molecules, meaning that one portion of the molecule is soluble in water and another portion is not.

• Scientists have concluded that prokaryotic life forms preceded the more complex eukaryotes. 
• All organisms on Earth are classified into two basic cell types. "Kary" means nucleus, "Pro" means "before," and prokaryotes have DNA in a freely floating ring that is not encased in a nucleus. 
• "Eu" means "true," and eukaryotes have DNA arranged in chromosomes and encased in a nucleus. 
• Fossil evidence indicates that prokaryotic cells first existed on the earth, prior to the arrival of the eukaryotes. 
• Though they lack skeletons, a few groups of single-celled organisms have hard portions or secrete hard shells and so appear in the fossil record. 
• This record is the best indication of prokaryotes' and eukaryotes' relative ages.
  

Species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups. Interbreeding also called as hybrid is the result of combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. 

In 1924, the Russian biochemist Aleksandr Oparin proposed that life could have developed through gradual chemical evolution in a “primordial soup.” This theory was independently proposed by English geneticist J.B.S. Haldane, also in the 1920s. This theory states that a mixture of organic molecules could form in an oxygen-deprived environment through the random interactions of small molecules, with energy provided by sunlight and lightning. This theory is not without controversy. 

RNA is capable of catalyzing a number of chemical reactions, including the polymerization of nucleotides. RNA is uniquely able both to serve as a template for and to catalyze its own replication. Consequently, RNA is generally believed to have been the initial genetic system, and an early stage of chemical evolution is thought to have been based on self-replicating RNA molecules—a period of evolution known as the RNA world.

Cyanobacteria are thought to be the first aerobic photosynthesizers evolved which gradually increased the oxygen portion of atmosphere changing it into oxidising one. The aerobic respiration was thus helpful for the animals to survive.