How did cells first appear on earth?

In order for the first cell to emerge, it needed to have both a way to replicate itself and proteins and enzymes to protect it from the outside world.

Since the complexity and degree of information found in the cell have been discovered, the notion that simple cells just happen by chance has long since been abandoned.

One theory holds that life originated from RNA, and proponents of this theory contend that RNA served as the basis for both the information-storing capacity of modern DNA and the enzymatic functions of modern proteins. However, the synthesis of RNA nucleotide bases has proven to be either extremely difficult or impossible under conditions that are representative of prebiotic life, and RNA's capacity to function as proteins is extremely limited.

Henry Quastler first proposed the DNA model in 1964. The challenge lies in the extraordinarily high probability of obtaining information about DNA and related proteins simultaneously and at the same location (Yockey Information Theory and Molecular Biology, p. 247).

When the complexity of DNA and proteins became apparent, Aleksandr Oparin proposed that natural selection could operate on prebiotic structures (Oparin Genesis and Evolutionary Development of Life, p. 146). Oparin's theory was contested because proteins are not known to code for DNA or information. The coacervate protocell theory dates back to the 1920s and postulated that proteins originated first. The theory went like this: soap bubble-like circles of proteins formed the first cells, then the proteins formed a system of self replication.

The earliest cells had to have both complex proteins and complex information needed to replicate both the proteins and the information, and none of the theories—protein first, DNA first, or RNA first—can explain the origin of complex information required for life.

Intelligence appears to be necessary for the information needed for life, and there is no scientific basis for the concept of intelligence in the first place.

The short answer is, "We don't know for sure." However, there are a number of theories that suggest a way forward, which I will outline below in order of increasing popularity:

According to some scientists, the accidental creation of a single molecule of self-replicating RNA (similar to DNA) in the world's oceans led to the eventual creation of cells. This is the theory that most scientists now hold. Life evolved by accident, from molecules forming randomly in the ocean.

2. Life originated elsewhere. This theory, which is held by a large number of science fiction enthusiasts as well as scientists, postulates that life never started on Earth (perhaps it started on Mars or an asteroid), and that some of this life struck Earth's surface in the form of a meteor. Of course, we are not talking about little green men here, but rather unicellular bacteria; it has already been demonstrated that some bacteria can survive in space when frozen, so this theory, though implausible, may still explain how life first appeared on Earth.

I hope that was helpful.

One widely accepted theory, the RNA world hypothesis, suggests that self-replicating RNA molecules were among the first forms of life; over time, these primitive structures evolved into more complex structures, which in turn led to the emergence of cellular life forms through processes like chemical evolution and natural selection. The precise origin of cells on Earth remains a topic of scientific research and debate.