How I became a marketing manager…

Well, I am still not exactly sure how this series of events came to unfold while I was fully conscious in the meeting, but somehow I have found myself in charge of a major re-branding and marketing drive for the company I work for…
Now this could easily be described as just another bunch of extra work to fill my empty hours, but as it turns out, I have no formal qualifications in the field… Luckily, however, I know quite a few people who work in marketing and will be making full use of their brainpower, but still, how did that happen, and this brings me to my next point, how often doesn’t it happen that you end up doing alot of work outside of the scope of your position within the company that you work for?
I find myself delving into fields that I used to have a passable working knowledge in, and learning that pretty much everything has changed, yesterday, and will do so again, tomorrow… While this remains an exciting field, I am forced to ask, how do you do it? How do you stay abreast of all the latest developements in a field, where everything you know is outdated by the time you know it? At least in IT you have a few weeks leeway, but here, as soon as it is discovered, it is done, killed and you have to move on… Innovation is no longer just a good idea, but a requirement. I find myself looking at Search Engine optimization and Social Media marketing, which are both quite manageable, but at the same time I have to create a whole new image and division in the company while marketing an entire new line of products and services from us, having not worked with those industries in four years…
So basically, time for an intense learning curve, catching up, new ideas and such… So two things then: a) How often and how are you expected to work outside of your field, and b) Are you in marketing and looking to help me with Social Media Marketing?