Some outcrops reveal round pillow structures, showing that the basalt lavas erupted under water.
Based on radiometric dating, long-age geologists say that the basalt lavas erupted 1,745 million years ago4 and were metamorphosed some 1,700 million years ago.5 Many people, including many scientists, accept these dates as absolute truth.
For example, the calculated “age” could be taken as the “date” of metamorphism, or it could be the “age” of the original volcanic (or sedimentary) rock, or something in between, or something else.
The calculated ages for all the individual samples from the dating method turned out to be vastly different (see box, “Calculating the ages”, below), even for those closely spaced samples from the same outcrop of the same lava flow.
Geologists calculate an “age” using the measured amount of a “daughter” isotope (e.g.
argon) and its corresponding “parent” isotope (e.g. However, before this calculation can be made, it is necessary to assume how much of the “daughter” and “parent” were present when the rock formed.
Clearly, the calculated ages are useless for dating any event.
potassium-argon (K-Ar) “ages” calculated for each of the 27 amphibolite samples from Grand Canyon ranged from 405.1 ± 10 Ma (million years) to 2,574.2 ± 73 Ma.
Indeed, of the isochron “ages” corresponds to the “date” for any theorized geologic event—neither the original lava eruptions nor the subsequent metamorphism.Among these volcanic layers are distinctive dark-coloured rocks called amphibolites3 (figure 3).These were once flows of basalt lava, up to tens of metres thick (figure 4).During several raft trips through Grand Canyon, many samples of these “Brahma” amphibolites were collected from various outcrops in the Inner Gorge.6 These included seven samples from a single amphibolite body (figure 5).7 All the samples were sent to two well-respected commercial laboratories for radioisotope testing.8 Both laboratories use standard, best-practice procedures on state-of-the-art equipment and routinely provide accurate and repeatable measurements of the required isotopes.It is important to realize that the laboratories do not measure the “age” of the rocks but the isotopes in them at the present time.The crystalline rocks of the Inner Gorge are below the horizontal strata of the main canyon walls (after Austin, ref. The problem is that we don’t know whether these assumptions are reasonable (because they are not provable), and it is especially awkward for metamorphic rocks.Geologists overcome this problem by “interpreting” the result.That is a six-fold difference, for samples that should be of similar age.Note that the error estimates (the ± numbers) are small compared with the age.Deep below the rim, the crystalline basement rocks tower above the turbulent Colorado River.Official publications say these rocks are more than a billion years old, but when the methods used to date them are carefully examined, a totally different story is discovered.