Big data wasn't always big data. It used to be little data, and it would byte everything (bad pun, sorry). 22 years ago, the first online advertisement was generated, birthing the online marketplace and consumer footprints simultaneously. Not only have the advertisements, audiences, or technologies advanced, but the measurements for the success of online ads have improved as well.
Image Source: By Camelia.boban (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons