Cannabis sativa is a very old plant. A study conducted in 1996 reported that humans created baskets out of C. sativa in Czech Paleolithic sites from nearly 26,000 B.C.E.  This was during the Pleistocene epoch (a.k.a. Ice Age). Some 6,000 years ago, in the Neolithic epoch in what is now Taiwan, evidence of C. sativa highlighted the plant’s use in textile manufacturing.  Historical accounts point to the cultivation of cannabis for fiber for use in manufacturing textiles and paper. China, it’s said, first domesticated C. sativa, and archaeologists believe that by circa 6,500 B.C.E., its widespread cultivation made it economically important.  China also invented paper making, and scraps have been dated to circa 140 to 87 B.C.E.  These types of materials were unearthed in a tomb that preceded Emperor Wu’s sovereignty circa 104-87 B.C.E. Therefore, the originally hypothesized timeframe of paper’s invention needed to be dated further back in time. 
While fibers labeled as hemp can be differentiated from those of other plants through scientific characterization, often, no lab tests are conducted, and yet, the fibers are still “called ‘hemp’ largely because of their context in early Chinese remains. If these same fiber samples had been recovered in western Europe rather than China, they might very well have been assumed to be flax rather than hemp, as flax also had a long history in ancient Europe.”  Also, it should be noted that the Chinese medical use of cannabis is thought to often refer to seeds, so it’s best not to jump to conclusions that the historical descriptions relate to flower. Nevertheless…
Hemp fibers seem rather ubiquitous in archaeological remains, as textiles like cords, rope, cloth, and shoes have been recovered.  The dead have been found buried in hemp-containing cloth, and crypts were bolstered with the plant’s fibers.
The use of cannabis medicinally traces back to the enigmatic figure called Shen Nung, who is considered the “father” of Chinese agriculture. Alongside the various spellings (e.g. Shennong) of this gentleman’s name are varied allegorical accounts. The Wikipedia page, for example, says that Shennong means “divine farmer,” and that Shennong was a mythological Chinese deity. The U.S. National Library of Medicine, however, states that Shen-Nung was a legendary emperor who “tasted hundreds of herbs to test their medicinal value.” Another site says that he “may have existed as a real person, but he was also a god.” God, human, human-god.
In a historical chronology of cannabis, Ethan Russo reports that circa 2,700 B.C.E. marks the timeframe that Shen Nung noted the “hallucinatory effects, appetite stimulation, tonic and antisenility effects” of cannabis.  The world’s first pharmacopoeia, called pen-ts’ao ching, referred to the orally handed down methods of Shen Nung’s application of cannabis for conditions such as “rheumatic pains, [intestinal issues], disorders of the female reproductive system, [and] malaria,” as well as absent-mindedness.  This pharmacopoeia is said to signify the first mention of cannabis as being psychoactive. The passage reads: “Ma-fên (the fruits of [cannabis]) … if taken in excess will produce hallucinations (literally ‘seeing devils’) … over a long term, it makes one communicate with spirits and lightens one’s body.” 
The first surviving Chinese dictionary, called the Erh-Ya, thought to date from the 3rd century B.C.E., reported that male plants best produced fiber, while the females led to intoxication. 
The founder of Chinese surgery, Hua T’o (117 – 207 C.E.), prepared cannabis to be ingested with wine as an anesthetic during surgery.  A stash of cannabis was found in the Yanghai Tombs that a global-research effort dated to near 700 B.C.E.  Incredibly, this stash contained delta-9-tetrahydrocannabinol (THC), cannabinol (CBN), and tetrahydrocannabinolic acid (THCA) synthase, the enzyme that catalyzes the formation of THCA.
So, did our early ancestors in ancient China smoke or ingest cannabis flower or resin? Like many things in life, we might not get a firm answer. But it seems pretty clear that ancient Asia cultivated the plant for various applications, something we’d be wise to adopt today, asap, instead of incinerating good biomass that might have many other functions or growing a plant for one molecule.
- Adovasio, J, et al. “Upper Palaeolithic Fibre Technology: Interlaced Woven Finds from Pavlov I, Czech Republic, c. 26,000 Years Ago.” Antiquity, Vol. 70, no. 269, 1996, pp. 526-534. [journal impact factor = 1.656; cited by 87 (ResearchGate)]
- Li, H-L. “An Archaeological and Historical Account of Cannabis in China.” Econ Bot., vol.28, no.4, 1974, pp. 437-47. [journal impact factor = 1.109; cited by 143 (ResearchGate)]
- Fleming, M. and Clarke, R. “Physical Evidence for the Antiquity of Cannabis sativa L.” Journal of the International Hemp Association, Vol. 5, no. 2, 1998, pp. 80-93. [journal impact factor = N/A; cited by 55 (ResearchGate)]
- Russo, E. “The Pharmacological History of Cannabis.” Handbook of Cannabis, edited by R. Pertwee, Oxford University Press, 2014. [cited by 11 (ResearchGate)]
- Touw, M. “The Religious and Medicinal Uses of Cannabis in China, India and Tibet.” J Psychoactive Drugs, vol. 13, no. 1, 1981, pp. 23-34. [journal impact factor = 1.740; cited by 99 (ResearchGate)]
- Li HL. “Hallucinogenic Plants in Chinese Herbals.” J Psychedelic Drugs, vol. 10, no. 1, 1978, pp. 17-26. [journal impact factor = 1.740; cited by 16 (ResearchGate)]
- Russo, E. “History of Cannabis and its Preparations in Saga, Science and Sobriquet.” Chemistry & Biodiversity, vol. 4, 2007, pp. 2624–2648. [journal impact factor = 1.449; cited by 204 (ResearchGate)]
- Russo, E. et al. “Phytochemical and Genetic Analyses of Ancient Cannabis from Central Asia.” Journal of Experimental Botany, vol. 59, no. 15, 2008, pp. 4171–4182. [journal impact factor = 5.360; cited by 87 (ResearchGate)]