The phrase "extensive glaciation" refers to a period of time when large areas of land are covered by thick layers of ice, known as glaciers, due to cold temperatures. Full definition
The current ice age is thought to have begun about 2.5 million years ago, and has alternated between periods of extensive glaciation, known as «glacial periods», and periods of more modest glaciation, like we have today, known as «interglacial periods», roughly every 100,000 years or so. (globalwarmingsolved.com)
The second was the crude graph by Scotese which is (in its original form), not proxy based, but merely assigns a warm temperature for periods without glaciation, and a cool temperature for periods with extensive glaciation. (skepticalscience.com)
Extensive glaciation took place around 2.2 billion years ago, in the Paleoproterozoic era, and it seems plausible that global ice cover occurred then, Sohl says. (giss.nasa.gov)