Google reported in 2011 that there were over a billion downloads
of Google Earth. That includes downloads of the Google Earth
desktop client, mobile apps and the Google Earth plug-in.
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A Google Earth plug-in is a plug that automatically brings you to Google Earth.
Answer#2
Actually, the Google Earth plugin is an embedded version of Google Earth that runs within the web browser.
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One uses Google Earth to get directions as Google Earth provides
geographical information about places on the Earth. Google Earth
was released twelve years ago in 2001.