Everything these so called scientists say is really just a wild ass guess.
It’s a guess based on the evidence gathered.
It’s a far more likely guess than dinosaurs aren’t real and the Earth is 6,000 years old.
It's much more than that.
In scientific terminology, a confirmed observation is a fact.
Facts in this case include geological strata, fossils, DNA, isotope decay rates, etc.
In scientific terms, an explanation which can be falsified is called a hypothesis, not a "wild ass guess".
If a hypothesis passes tests intended to falsify it, then it can be accepted as a confirmed theory.
An example is Darwin's 1859 evolution hypotheses.
Since 1859 it has been tested and modified many times, but his basic ideas of 1) descent with modifications and 2) natural selection as driving evolution are today considered confirmed theories with many observed facts.