The organisms which appeared on earth first was bacteria.
<u>Explanation:</u>
The first-ever living organism on Earth was a bacteria known as cyanobacteria. It is believed by scientists that it first formed around 3 billion years ago.
When the Earth was first formed, it was inhospitable for a long time until 3.8 billion years ago approximately, the core cooled down and the level of oxygen had risen. This, along with photosynthesis resulted in the formation of Cyanobacteria.
These organisms were capable of carrying out the process of photosynthesis by which they prepared their food. These were known as common ancestors. All the living organisms thereafter are known to be their descendants.
The first living beings on the Earth, were the single-celled organisms called as micro-organisms or the microbes that lacks a cell membrane or cell nucleus known as Prokaryotes, seems to be appeared first on the Earth almost 4 billion years ago, which was just a few 100 million years subsequent to the Earth formation itself. Considerably, the longest part of the life history on the Earth, thus, involved the biochemical development of these unicellular micro-organisms, such as bacteria and archaea.
The answer is if the niches of two organisms were moved to the other ecosystem they would compete with one another for the same food and other resources in the environment. Eventually, one species would be likely to outcompete and replace the other.
