Separate from how life has evolved on Earth (which is explained by the theory of evolution -- ToE) is the fact that life has changed over time.
Once upon a time (and we won't worry about the absolute value of that time -- that is for the dates and dating forum) there no multicellular creatures. Later there were some that we might tag as "primitive" but they bore hints of current groups but there were no fish, reptiles, mammals or birds.
Later there were fish but no birds,reptiles or mammals.
Finally there were representatives of all of todays major groups of living things. In addition, as we examine those that died more recently they look more like those extant today.
Thus, over time, the forms of life changed. This is the fact of evolution.
This has been discussed before, of course.
But we have a few here now you haven't grasped the two basic sets of evidence which any idea about life on earth has to explain. This is one of the sets of evidence.
The other is, of course, the actual age of the Earth and each part of it's geology.
Since there are a number of discussions going on about some things which are, in comparison to these two points, I thought it would be useful to revisit this one.
Anyone who wishes to disagree with evolution must first explain the series of changes that we observe in the forms of life on earth.
This should go into Biological Evolution