I don't know where and how it evolved. Would you be kind to share with me the history of SEM? Thanks

Search engine marketing, or SEM, is a form of Internet marketing that seeks to promote websites  by increasing their visibility in search engine result pages (SERPs) through the use of search engine optimization, paid placement, contextual advertising, and paid inclusion.
 Usage of the term "search engine marketing" has been inconsistent. The trade association Search Engine Marketing Professional Organization (SEMPO) includes search engine optimization (SEO), and SEO is also included in the industry definitions of SEM by Forrester Research, eMarketer, Search Engine Watch, and industry expert Danny Sullivan.
The term "Search Engine Marketing" was proposed by Danny Sullivan in 2001  to cover the spectrum of activities involved in performing SEO, managing paid listings at the search engines, submitting sites to directories, and developing online marketing strategies for businesses, organizations, and individuals.