There's no standard atheist answer to these questions. There's really no standard atheist answer to anything. There's no atheist dogma or doctrine, no supposedly inerrant textbook, no creed to recite. Atheism is just a single conclusion. You may draw other conclusions from that one, but they're your own.
And here's what so many people don't consider: there may not be an available answer to every question. We may never know it all. What more people do realise is that just because someone has an answer doesn't mean that it's correct. I'm glad to see that you doubt the god answer even without a satisfying alternative.
The Big Bang was what happened when all the matter in the universe was compressed to one point and then started expanding outwards. It's still happening, and it's even speeding up. We've worked that much out by watching some of that matter whizz apart. Before that point, we don't know what all the matter and energy was doing.
Firstly there may not even be a proper "before" if the Big Bang started time as we know it. Causality gets a bit wobbly when chronological order and displacement are not reliable.
Leaving that aside, the creation of matter or energy breaks the law of conservation. You could make an exception and say that matter can be created by some unknown process and is then permanent, I suppose. If the law is 100% true, though, then all matter and energy has existed forever. I'm fine with that.
Before the Big Bang theory the leading concept was an eternal "steady state" universe. Perhaps there's another universe like that which is the source of all the matter in this universe. Perhaps the pre-Big Bang singularity was a discrete packet of matter ejected from that other universe. Free of the confines of its origin, it relaxed and expanded.
If an eternal universe doesn't appeal to you, why not an eternal series of finite, sequential universes? As each one "dies", the matter somehow collects and starts over. Not necessarily by a Big Crunch, as the discovery of accelerating expansion put paid to that idea, but perhaps by everything draining out when some barrier or membrane finally breaks.
We can carry on this line of thinking if you like (the next step would be to discuss how the above could satisfy the second law of thermodynamics) but my point is that there are plenty of other theories for the origin of matter and energy, one being that it's eternal and needs no origin. This is no less plausible than an intelligent superbeing with the same quality.
I hope having a few more possible answers will make the questions a bit more pleasant as they run around in your head. It won't stop them from running though, because they run through the head of everybody who doesn't utterly accept some religious answer.
Contrary to what anyone tells you, we do not know our ultimate origin, or whether we have one. This doesn't stop us from wondering, observing and theorising. Which is great, because doing all that is fun.
- SmartLX
Something which was very nearly a man (or woman), but was technically an ape according to our modern classification system.
The offspring was very slightly mutated; it was just different enough from its ape parents to get across our arbitrary line and be properly human. Whatever was different, it was probably something beneficial like longer legs, stronger hands or a bigger brain.
Of course, the first human didn't care about classifications and it didn't know it was human. We just think about it this way in retrospect.
- SmartLX
Miracles, until proven to have been impossible and yet to have happened, are just interesting stuff that might have happened.
I can't explain how the world was created, not least because I don't know whether it was created. God is one hypothesis for its origin, and a very unlikely one at that; there are many others. The universe might even be eternal, and have no origin at all.
Humans were not created, they evolved over millions of years from increasingly human-like animals. The male and female sexes evolved too, much earlier in the piece.
- SmartLX
Let's go through this very carefully.
- We have about 8,000 years of recorded human history. Humans are the only creatures who have ever deliberately recorded it. All time before that is referred to as PREhistory for a reason; the universe pre-dates recorded history. By about 15 billion years.
- The Big Bang was a sudden expansion of matter. It did not create any heat, because all heat was contained within it; it merely dispersed heat like it did matter. It did not necessarily create anything, since nothing stops the matter from having existed before the Bang. It did not destroy anything either, because there was probably nothing outside the Bang that it could destroy. Comparing the Big Bang to an explosive detonation is a gross oversimplification.
- Present-day black holes do contain vast amounts of matter compressed to a single point, or singularity. It happens when the gravity of an object is great enough to overcome the magnetic fields keeping the atoms apart. Current physics do allow for this.
- Even if time as we know it resulted from the Big Bang, it's not necessarily all the time there's ever been. What if another system of time and space existed, and the Big Bang spawned from this? Perhaps another universe?
An atheist doesn't know how the heck the Big Bang happened, because we haven't found enough evidence to make any theory remotely certain. I'm comfortable with that. If I adopted one hypothesis as the truth now, I'd have to fault every other theory out there without any support at all.
Finally, don't take offence but to assert beyond doubt that a God is responsible for something merely because of the absence of known alternatives is the very model of an argument from ignorance.
I won't cover abiogenesis (the origin of life) here, because neither has MrPeters.
- SmartLX