Hemp has been cultivated since the dawn of civilization. Actually, our Paleolithic ancestors were weaving baskets with the stuff before civilization. To strip the fibers for textiles and other uses, people soaked hemp in standing/slow bodies of water—after a few days, the plant material trapping desired fibers explodes out as sludge.  This process is known as water retting. A traditional method for thousands of years, it’s now been mostly replaced with other methods. Recently, researchers have noted that phytocannabinoids are released during water retting. [1,2] Thus, there is a historical record of hemp’s cultivation and manufacture lying at the bottom of some lakes. 
Schmidt et al  focused on how to measure it. Cannabinol (CBN) is a major degradation marker for cannabis; tetrahydrocannabinol (THC), for example, degrades directly to CBN in unfavorable conditions (such as the bottom of a lake). A previous study in 2013 confirmed CBN in lake sediment from the French Massif Central indicating consistent retting activity from 470–870 AD and 1180–1860 AD. [1,2]
The goal in the more recent study was to develop “a fast and accurate high-throughput screening of sediment samples” capable of efficiently tracking ancient hemp retting via CBN.  The researchers thereby selected high performance thin layer chromatography (HPTLC) coupled with electrospray ionization (ESI) mass spectrometry (MS). The sediment samples were extracted from a “small lake in Northern India, covering a period from 2220 BCE to 1390 CE.”
The process is summarized in the figure from the (open access) study as seen below:
The CBN content in ancient sediment varied from 99.2 ng/g to 486.5 ng/g. Peak CBN occurred at a sediment depth of 260 cm (roughly 8.5 feet). From roughly 262 cm up to 209 cm (almost 7 feet), CBN was highest, reflecting the most intense water retting period in the area’s history. Specifically, these depths reflect the historical period of 480 BC to 1050 AD.
Thus, the authors conclude that the method provides a “helpful tool to track ancient hemp retting activities.” Ultimately, this technology illuminates the ancient dance of hemp and humanity through history.
- Schmidt T, et al. Identification and quantification of cannabinol as a biomarker for local hemp retting in an ancient sedimentary record by HPTLC-ESI-MS. Analytical and Bioanalytical Chemistry. 2020;412:2633–2644. Impact Factor: 3.637 Times Cited: N/A
- Lavrieux M, et al. Sedimentary cannabinol tracks the history of hemp retting. Geology. 2013;41(7): 751-754. doi:10.1130/G34073.1. Impact Factor: 4.768 Times Cited: 37