How has the extraction of tarsands changed over time?

Tar sands (also called oil sands) are a mixture of sand, clay, water, and bitumen.[1] Bitumen is a thick, sticky, black oil that can form naturally in a variety of ways, usually when lighter oil is degraded by bacteria.[2] Bitumen has long been used in waterproofing materials for buildings, and is most familiar today as the binding agent in road asphalt. However, most of the bitumen produced from tar sands is refined and mixed with lighter oils to produce synthetic crude oil that can be further refined and used in much the same way as typical crude oil.[3]

Because bitumen is very thick and does not flow easily,