Science can be sure of many things

Science does keep changing, what with Newton's ideas being replaces by those of Einstein, and quantum mechanics messing up simple ideas of what matter was made of.  But not really.  This isn't the way science works.

Science involves two things which are combined to try and help understand reality:  the first is an hypothesis, an idea about what is happening and the second is data.  What is seen to happen - the data - is used to test ideas about what is actually happening.  Science keeps progressing in terms of what is seen to happen, and once enough reliable data has been gathered what is seen to happen rarely changes, whereas ideas about what is actually happening can often change.

For example, in the study of genetics and inheritance data about the way inherited characteristics behave has been known for a long time.  It has been known that the basis of inheritance has to be digital, not continuous, because individual characteristics don't blend, they retain their existence from generation to generation: this is why features present a grandparent can re-appear in grandchildren while not visible in the children of the grandparents: a feature can require two copies of inheritance material to be visible.  This feature can be only present in one copy in the first generation, but two copies can randomly come together in the second generation. We know based on data that genetic material in humans is paired up in most cells, and that it contains digital information.

There were all kinds of hypotheses about what the genetic material consisted off, and eventually even more data showed that it was DNA.  Once found, DNA became a new part of the data, part of the known.  It's a fact about human existence: science isn't going to find humans that don't have DNA.

Another example is gravity.  Newton's model of gravity was based on data about planetary (and other) movement.  We knew that the Earth orbited the Sun at that time.   More precise data was one of the things that led to Einstein's model of gravity, but that was never going to show that the Earth did not orbit the Sun.

Science does progress, and does lead to things that it is entirely reasonable for us to consider true and not provisional.  What changes in science is the understanding of mechanism, of what is happening behind the scenes.  In 1000 years we will still be saying that the Earth orbits the Sun (unless we have moved the Earth!).