Apple CEO John Ternus marked his first day in the top job at the tech giant on Tuesday, with the company embarking on a new era after former CEO Tim Cook stepped down from the role after 15 years.Cook, who will remain with Apple as the company's executive chairman, saw the diversification of its product offerings with the release of devices including the Apple Watch and AirPods, as well as its growth into services through offerings like Apple Pay.The company also saw explosive growth, becoming the first publicly traded U.S. company to surpass $1 trillion in market capitalization in 2018 – whic...