Blogs facilitate online debates and discussions for millions of people around the world. Identifying the most popular and prevailing topics discussed in the Blogo-sphere is a crucial task. This paper describes our novel approach to the quantification of the level of topic propagation in the Blogosphere. It tries to answer one key question: How many people should know about a subject before it becomes prevalent? Our model uses graph-theoretic representations of the Blogosphere's link structures that allows it to deduce the Percolation Threshold, which is then used in the quantification and definition of a prevalent or 'Global' topic. We applied our approach and analysed the social structure of the ICWSM data collection to find the answer.