Or, more importantly, what did they demonstrate?
"EXCESS ARGON": THE "ACHILLES' HEEL" OF POTASSIUM-ARGON AND ARGON-ARGON "DATING" OF VOLCANIC ROCKS
For more than three decades potassium-argon (K-Ar) and argon-argon (Ar-Ar) dating of rocks has been crucial in underpinning the billions of years for Earth history claimed by evolutionists. Critical to these dating methods is the assumption that there was no radiogenic argon (40Ar*) in the rocks (e.g., basalt) when they formed, which is usually stated as self-evident. Dalrymple argues strongly:
The K-Ar method is the only decay scheme that can be used with little or no concern for the initial presence of the daughter isotope. This is because 40Ar is an inert gas that does not combine chemically with any other element and so escapes easily from rocks when they are heated. Thus, while a rock is molten, the 40Ar formed by the decay of 40K escapes from the liquid.1 However, this dogmatic statement is inconsistent with even Dalrymple's own work 25 years earlier on 26 historic, subaerial lava flows, 20% of which he found had non-zero concentrations of 40Ar* (or excess argon) in violation of this key assumption of the K-Ar dating method.2 The historically dated flows and their "ages" were:
Hualalai basalt, Hawaii (AD 1800-1801) 1.6±0.16 Ma; 1.41±0.08 Ma
Mt. Etna basalt, Sicily (122 BC) 0.25±0.08 Ma
Mt. Etna basalt, Sicily (AD 1972) 0.35±0.14 Ma
Mt. Lassen plagioclase, California (AD 1915) 0.11±0.03 Ma
Sunset Crater basalt, Arizona (AD 1064-1065) 0.27±0.09 Ma; 0.25±0.15 Ma
Far from being rare, there are numerous reported examples of excess 40Ar* in recent or young volcanic rocks producing excessively old K-Ar "ages":3
Akka Water Fall flow, Hawaii (Pleistocene) 32.3±7.2 Ma
Kilauea Iki basalt, Hawaii (AD 1959) 8.5±6.8 Ma
Mt. Stromboli, Italy, volcanic bomb (September 23, 1963) 2.4±2 Ma
Mt. Etna basalt, Sicily (May 1964) 0.7±0.01 Ma
Medicine Lake Highlands obsidian, Glass Mountains, California (<500 years old) 12.6±4.5 Ma
Hualalai basalt, Hawaii (AD 1800-1801) 22.8±16.5 Ma
Rangitoto basalt, Auckland, NZ (<800 years old) 0.15±0.47 Ma
Alkali basalt plug, Benue, Nigeria (<30 Ma) 95 Ma
Olivine basalt, Nathan Hills, Victoria Land,
Antarctica (<0.3 Ma) 18.0±0.7 Ma
Anorthoclase in volcanic bomb, Mt Erebus, Antarctica (1984) 0.64±0.03 Ma
Kilauea basalt, Hawaii (<200 years old) 21±8 Ma
Kilauea basalt, Hawaii (<1,000 years old) 42.9±4.2 Ma; 30.3±3.3 Ma
East Pacific Rise basalt (<1 Ma) 690±7 Ma
Seamount basalt, near East Pacific Rise (<2.5 Ma) 580±10 Ma; 700±150 Ma
East Pacific Rise basalt (<0.6 Ma) 24.2±1.0 Ma
Other studies have also reported measurements of excess 40Ar* in lavas.4 The June 30, 1954 andesite flow from Mt. Ngauruhoe, New Zealand, has yielded "ages" up to 3.5±0.2 Ma due to excess 40Ar*.5 Austin investigated the 1986 dacite lava flow from the post-October 26, 1980, lava dome within the Mount St. Helens crater, which yielded a 0.35±0.05 Ma whole-rock K-Ar model "age" due to excess 40Ar*.6 Concentrates of constituent minerals yielded "ages" up to 2.8±0.6 Ma (pyroxene ultra-concentrate).
See the list of citations at the bottom of the first link for the various Geologists who found bad dates and excess argon.