1) Lets say the world is 4.5 billion years old. Would it be possible for macro evolution?
Yes, the 3.8 billion years or so that life has been here certainly allow for evolution above the species level.
2) Why hold to a 6,000 year old Earth. When trees have been dated older than that? (I think the Earth is 50,000 - 20,000)
We all know why, because scientific evidence is not the most important thing to people who believe in a young earth. The most important thing is a literal reading of the Bible, adding up geneaologies and then attempting to pull together whatever appearance of 'science' they can find to support this pre-determined conclusion.
In my opinion the geologic column is evidence for evolution. Cyanobacteria is found in old rocks, but in these same rocks no humans, no mamals no nothing besides simple multicellular organisms have been found. how do you explain this?
They don't, at least not in any way that stands up to even elementary examination. I have to say I'm curious how you would understand this with a 50,000 year old earth.
4) Is it possible to believe in YEC and believe that evolution is possible?
No, you can't have universal common descent in 6,000-10,000 years. YECs do however believe in a completely different form of evolution, explosive divergence after the flood, with almost daily speciation events.
I have been reading quite a bit in this forum. One thing which caught my eye was the speed of light, and that it was faster in the past. There was a graph showing that 6,000 years ago the speed of light was much quicker. however, if the speed of light is too quick it will make things in the universe unstable. How do you explain this?
Answersingenesis lists this as one of their
arguments that should be avoided. The is no evidence that the speed of light has changed by the orders of magnitude that are required to get light the vast distances required in the 6,000-10,000 time limit that YECs have.
Changing the speed of light alters various other things which would result in chaos and would require more divine interventions to fix. There is quite simply a complete breakdown in the laws of physics in a young cosmos.
It is for reasons such as these that no serious cosmologist/physicist even entertains these ideas. Nobel Prize winning physicist Murray Gell-Mann for example remarked that the scientific credibility of a young universe is comparable to (if not perhaps weaker than) that of a flat earth.