Some (although not all) creationists often present a really strange argument with the intent of discrediting science: They argue that science keeps "constantly changing". In some pathological cases some creationists have gone even so far as to state that they do not allow their children to go to school because of this reason.
(One cannot help but to notice the hypocrisy of these people not having any trouble in using the products of this "ever changing science" to divulge their opinion of it, including things like computers, internet networks, video cameras, video editing software, and so on. Likewise they seem to be living quite comfortably in modern houses with running water, electricity, fridges, etc. All products of this discredited "constantly changing" science.)
The simplest answer to this argument is, of course: Yes, that's called progress. It's the reason we don't live in the bronze age anymore.
The argument makes absolutely no sense. A good way to illustrate the ridiculousness of the argument is with an analogy:
Suppose that the police investigates a murder. This chain of events happens:
Now, imagine that they catch the killer, and on the murder trial the defense attorney makes this argument:
"The police keeps constantly changing their story. The earliest time estimate for the murder was first 2pm, then it was 2:15, then 2:30... And what about the end estimate? First it was 3pm, then 3:30, then 3:10... And this not to talk about their suspects. First they suspected the wife, then a neighbor, then a visiting friend... Clearly the investigators have no idea what they are talking about. Their estimations keep changing. Clearly there was no murder, this whole thing is a lie and my client is innocent."
This defense attorney would probably not have a job for long. Even his client would probably think he's outright crazy.
Another example, more closely related to actual events, would be the measurement of the radius of the Earth: This radius has been estimated since antiquity (Eratosthenes was one of the first people to estimate the radius of the Earth using a scientific method), and its value has been refined during the entire history of humanity as technology has progressed. If someone were to argue that the Earth is actually flat because science is "constantly changing its mind on what's Earth's radius", people would justly think that this person is crazy.
The universe works in a certain way. So far it seems pretty clear that the universe works in a very consistent way, without its laws changing. We may not yet fully understand every single detail of how the universe works, but as we investigate we are getting closer and closer to the truth, narrowing down the possibilities. In some cases science might take a completely wrong path of deductions, but then it will discard it when it doesn't fit the facts.
There's obviously nothing wrong with this. Like when investigating a crime, estimations are narrowed as the phenomenon is investigated more and we get more useful data about it. Wrong ideas will be discarded and existing good ideas will be refined. Slowly we get closer and closer to understanding how the phenomenon really works. This is far from the "blind guessing" that the creationists are trying to argue.
The funny thing is that the "science keeps changing" was only the first part of the argument. The whole argument goes: "Science keeps changing, God is always the same."
The obvious question to that is, of course: If God doesn't change, why are there something like 30000+ denominations of Christianity in the world, some of them with really differing view than others? They will answer: "There's only one truth. We might not yet fully understand it, but if we study the Bible enough, and pray to God, we will."
So, when science searches for the one truth (about how the universe works) by investigation and study, that's somehow bad, but when Christians search for the one truth by investigation and study, that's ok. Double-think much?