The reasons why there are viruses on earth are:
If there is no death, there is no life.
Life depends entirely on the cycle of matter, and viruses are very important to the cycle of matter and species. The structure of the virus is simple but quite effective. Millions of years from now, there may be no humans left, but viruses will still be there.
Viruses are an important part of the ecosystem. More than 90% of organisms present in the oceans are microorganisms. These microorganisms produce about half of the oxygen on Earth, and it is viruses that make this process possible. Every day, phage viruses kill 20% of marine microorganisms and 50% of marine bacteria.
By eliminating microorganisms, viruses provide oxygen-producing plankton with enough nutrients to increase the rate of photosynthesis, which ultimately supports mostlife forms on Earth. When populations are very large, viruses tend to multiply quickly, destroying the population and creating space for other species to survive.
The virus enters the host cell and hijacks its replication vector to replicate. When this happens in germ cells, the virus code can be passed on to the next generation and they can combine permanently. Every organism susceptible to infection by a virus has the ability to absorb and use the virus's genes, and the disappearance of the virus will affect the evolutionary potential of all life on earth, including humans.
Viral components are estimated to make up 8% of the human genome, while mammalian genomes typically contain around 100,000 remaining virus-derived genes scattered throughout the genome. The viral code usually appears as inactive segments of DNA, butit is sometimes equipped with new, useful, even essential functions.
For example, in 2018, a research team discovered that a gene derived from a virus codes for a protein that carries messages between cells in the nervous system and plays an important role in the formation long-term memory.
There is also evidence that humans survive on DNA from an ancient retrovirus that infected our ancestors 130 million years ago, combined to give humans their current reproductive patterns .