Okay. Let' start with this one:
- 200,000 years ago: humans started looking like we do today
This is based on a hypothesis. Not sure which model ("Replacement Model" ??) the poster was referring to but the timeline is still widely contested and lacks any sufficient evidence to make it factual or supported by the heavy and convincing evidence the poster says exists. The science is all over the place on this one and some of the more recent "scientific" findings suggest that humans appeared sometime within the last 100,000 years. The popular models that are used in the hypotheses are complicated by inconsistencies in the fossil record.
The bottom line is, there is no hard evidence pointing to a verifiable time when homo sapiens first "evolved." In other words, no one really knows.
You're right. We don't know for sure. We know a lot. We know it's a lot more than 50,000 years ago. We know it's more than 75,000 years ago. But we keep finding new information. We just found a brand new species of an apparently intelligent humanoid recently. We didn't have that information before. http://www.guardian.co.uk/science/2010/mar/24/new-human-species-siberia
However, nobody in science and nobody who is a fan of the things science is finding expects that we've come up with the end-all answer to this or any other question. We are finding out new things all the time. Do you expect people to suddenly say "Well,this is exactly the way it was!" with certainty, knowing all the while that someone might dig up a new ancestor tomorrow and find out something completely new about our species. I don't think so. How many thousands of buried remains are out there from 50 or 100 thousand years ago? We have no idea. How many of those remains will actually be found? We don't know. But each set found may reveal something new. Or help confirm earlier suspicions. Or simply confirm earlier accepted assumptions.
Don't think that absolutes like exact dates are of huge importance. We're talking about spans of time that nobody can actually comprehend. We're talking about spans of time that contain so many variables that there is no way to pinpoint anything exactly. Without the convenience of calendars and written histories, we're stuck doing a lot of assuming. But we do know we're in the ballpark, age-wise. We do know a lot about the distribution of early humans, because we keep finding remains in some areas and never find them in others.
We can be more exact about more other types of dating. In the plant world, for instance, one plant of a holy species in Tasmania that cannot reproduce (it has three sets of chromosomes and is sterile) has been found that is, by all measurements, about 43,000 years old. I know that's hard to swallow, what with genesis and arks and all, but that's what they found. The same plant has been sprouting new suckers from its roots for that long. Not impressive enough? Aspen trees form colonies of genetically identical plants that are essentially one plant growing over and over. One such colony has been estimated to be 80,000 years old. If we were smart, we would ask it what people looked like when it was young.
Sadly the aspen are in the US and there were no people here that long ago.
Anyway, people may have looked like humans about 16 times longer than the bible claims, or they may have looked human 32 times longer. Plants exist that have been alive 13 times longer than the bible says the earth has existed. If you want something more recent, there are pines in the California Sierra's that, counting rings, mind you, are over 5,000 years old. That's younger than genesis, but a heck of a lot longer ago than the flood.
They are working on ways to date stuff, at least from more recent history, more accurately. Comparing tree rings and ice layers from the polar regions they have been working on ways to figure out what the weather was like each year on earth going back over half a million years. I don't know how many years they can go back now, but it is now possible to find a piece of wood buried in human ruins, look at it's rings, and determine very exactly what years it grew. And as we gather in more information, we will be able to go back further. With very exact dating, like 5,121 years ago and stuff.
We probably won't be able to tell you the month though.