# How was the onset of the Cambrian period dated?

What dating method was used to determine the beginning of the Cambrian, and what was its margin of error? Was only one fossil dated, or were a number of similar fossils used?

• It doesn't answer my question. I already knew the dating was radiometric. – Michael Walsby Mar 13 '20 at 13:35
• @MichaelWalsby other people don't know that until you say so. Can you add some more detail to your question? I think I can see what you are asking. While radiometric dating can generate the age of a given object, to determine the beginning or end of a period in geological history requires much more than that. – uhoh Mar 15 '20 at 14:39
• @uhoh i removed my comment,i still think the question needs some work. – trond hansen Mar 15 '20 at 17:02

Just to give some complementary informations from the other answer: the base of the Fortunian is indeed defined in eastern Canada on the basis of a trace fossil (which obviously cannot be itself dated since it is just an imprint), Trichophycus pedum. This trace fossil however being spread worldwide help correlating various sections throughout the world. One of such section is the Birba-5 well in Oman where the radiometric age was actually measured (at least the one currently considered as the proper age of the base of the Cambrian): volcanic ash bed BB5 could be dated using $$\ce{^{206}Pb/^{238}U}$$ radiometric dating at 541 +/- 0.63Ma, based on the analysis of 8 different zircon grains.