The Sphinx Erosion Bench: A Ratio, Three Dials, One Year

THE SPHINX EROSION BENCH · A RATIO, THREE DIALS, ONE YEAR
'These results were completely unexpected' (ch. 2)
Four seismic lines on the floor of the ditch, 1991: 1.8–2.5 m of weathered rock on three sides, 1–1.2 m behind the rump
the velocities and depths are the paper's; the ditch is drawn to the published envelope
the year is arithmetic on the ratio and three assumptions the book states and never dials
no one has drilled the floor; every dial here stands in for that core
walk the ditch · read the ratio · move the dials · price the rain

Evidence

fact ⇄ what kind of claim · live

'Circa 2500 BCE, at the latest' for the rump floor; '50 percent to 100 percent earlier', 7000 to 5000 BCE (1992); '2.7 times older... circa 10,000 BCE' and 'rates typically proceed nonlinearly... still older' (2016); Reader: Early Dynastic; Harrell: 'has not dug or drilled into this layer'

the book's words and its critics', cited by chapter and appendix

REPORTED

Dobecki & Schoch 1992: S1 1,285/3,205 m/s, 1.8–2.5 m; S2 1,260/3,184, 1.8–2.5 m; S3 1,039/2,502, 1–1.2 m; S4 1,426/—, 2–2.5 m (3–3.5 in places); S9 1,257/2,881, 1.2–1.5 m; S10: a cliff 8–9 m at 40 m east, water table at ~15 m ASL

the only instrumented measurement in the dispute; S4's sound-rock velocity did not survive the printed figure

MEASURED

d = k·τⁿ; τ_E/τ_W = (d_E/d_W)^(1/n); Δτ = τ_W·(ratio^(1/n) − 1); calendar years = Δτ / c; the book's 1992 and 2016 numbers reproduced from its inputs (4725–7350 BCE; 10,125 BCE) before any dial moves

the conversion is arithmetic; the bench does the book's sum first, then lets you change the terms

EXACT

Cairo today 25–28 mm/yr; Kuper & Kröpelin 2006: monsoon into the eastern Sahara 8500 BCE, up to ~100 mm/yr, retreat after 5300 BCE; Hayes 1965: sub-pluvial c. 5000–2350 BCE, Butzer 1971: aridity from 2350 BCE; Reader 2001: Khufu's quarries cut the runoff; Colman & Pierce 1981: age ratio between the thickness ratio and its square

the published climate frame and the published rind law; no rainfall figure exists for Giza's latitude in either wet phase

MEASURED

The baseline year, the exponent, the climate multiplier and the rain sensitivity as dials; a stepped rainfall proxy with its levels as dials; a drawn catchment and runoff coefficient; the quarries taking 95 %; profile shapes inside the printed ranges; interpolation between the lines

choices, shown as dials; the findings are quoted across their whole range

MODELLED

Whether a real depth ratio with no measured rate, no measured exponent and a borrowed baseline dates a monument to 7000, 10,000 or 4500 BCE, or only to 'before Khafre'

the one question this bench refuses to close for you

READING

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