Radiometric dating volcanic ash

The potassium-argon (K–Ar) dating method is often used to date volcanic rocks (and by extension, nearby fossils). Eleven samples were collected from five recent lava flows during field work in January 1996—two each from the 11 February 1949, 4 June 1954, and 14 July 1954 flows and from the 19 February 1975 avalanche deposits, and three from the 30 June 1954 flow14 (Figure 6).

Blocks weighing up to 1,000 tonnes were hurled 100 m (330 feet).

However, the most violent explosions occurred on 19 February 1975, accompanied by what eye-witnesses described as atmospheric shock waves.9 Blocks up to 30 m (100 ft) across were catapulted up to 3 km (almost 2 miles). Turbulent avalanches of ash and blocks swept down Ngauruhoe’s sides at about 60 km (35 miles) per hour.10 It is estimated that at least 3.4 million cubic metres (120 million cubic feet) of ash and blocks were ejected in 7 hours.11up If any of these assumptions are violated, then the technique fails and any “dates” are false.

The K–Ar method works on the assumption that the “clock” begins to “tick” the moment that the rock hardens.

That is, it assumes that no argon derived by radioactive decay was present initially, but after the lava cooled and solidified, the argon from radioactive decay was unable to escape and started to accumulate.

Fossils are almost never dated by radiometric methods, since they rarely contain suitable radioactive elements.

A common way of dating fossils (and rocks which do not contain radioactive elements) is by “dating” an associated volcanic rock. It depends on the rate at which radioactive potassium decays into the gas argon.

Because argon is a gas, it should escape to the atmosphere due to the intense heat of the lavas. All flows were typically made up of jumbled blocks of congealed lava, resulting in rough, jagged, clinkery surfaces (Figure 8).

Of course, no geologist was present to test this assumption by observing ancient lavas when they cooled, but we can study modern lava flows. The samples were sent progressively in batches to Geochron Laboratories in Cambridge, Boston (USA), for whole-rock potassium-argon (K–Ar) dating—first a piece of one sample from each flow, then a piece of the second sample from each flow after the first set of results was received, and finally, a piece of the third sample from the 30 June 1954 flow.15 To also test the consistency of results within samples, second pieces of two of the 30 June 1954 lava samples were also sent for analysis. No specific location or expected age information was supplied to the laboratory.

He has told us when that was, in His eyewitness account in the Bible’s first book, Genesis, so we know how old all the rocks are.

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