Germ Theory
Diseases used to be associated with paranormal powers or the wrath of gods in most cultures. The discovery of microorganisms and advancement of medicine may be our civilization’s greatest achievement.
Evolutionary biology was the main one
God’s an unfalsifiable claim, so there really isn’t anything that could test that hypothesis.
Pretty much any scientific test/discovery that counters anything in a religious text whose adherents view the text as completely truthful and literal. But sciencey stuff might not have much of an effect on religious folks who view their texts less literally.
But anyways… heliocentrism, germ theory, gravity, evolution through natural selection, probably a huge chunk of the field of archeology, plate tectonics, radiometric dating, probably the written language at various points in human history (but that’s not really a discovery), trans species organ transplants, decoding DNA, direct genetic engineering, CRISPR, radio telescopy.
Letter from Charles Darwin to Asa Gray (22nd May 1860)
With respect to the theological view of the question; this is always painful to me.— I am bewildered.— I had no intention to write atheistically. But I own that I cannot see, as plainly as others do, & as I shd wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.
On that note, what’s up with the obligate coprophagy of the koala? And their famously smooth brains? I’d make the koala, were it I in the high seat, but a kind and caring creator wouldn’t.
Religion exists for a number of reasons, but the primary purpose it serves an individual is as a foundation for their overall worldview.
“Faith” as many call it, serves to answer questions we don’t have answers to.
Where did we come from? Why are we here? What happens after we die?
Religion gives us comforting answers to these questions, and as these questions are ultimately unanswerable, can do so in perpetuity.
Religion has also tried to answer questions that we didn’t yet have answers for.
What are the sun, moon, and stars? Why are there tides? Why does it rain?
God was long accepted as the source of these things, and prayer was thought to be the best way have any influence.
But today we have answered basically all the major questions. We have a working model of the entire solar system, down to the weather on other planets. We figured out how to turn rocks into computers. All that’s left is the unanswerable.
As for where we come from, we’ve filled in a lot of gaps. Evolution is now the accepted answer for where Humans came from, now the question is where life itself came from, and if there’s life outside of Earth (and how much).
Philosophy has given us plenty of options for what our purpose is. There are plenty of ways to wrap your mind around your own identity without turning to the supernatural.
And our study of anatomy and neurology suggests that our conscious self ceases to exist after death, the only thing standing in the way of that belief is the very human tendency to be in denial of our own mortality.
