How the geo strata are identified as time periods

Just a nitpick; that's mostly but not 100% true. There are structures that form when sedimentary rocks lithify (turn into rocks), and in some cases those structures can be dated. (E.g. SHRIMP U-Pb dating of diagenetic xenotime in the Stirling Range Formation, Western Australia: 1.8 billion year minimum age for the Stirling biota. But it ain't easy, and requires recently depeloped instrumentation to handle incredibly tiny sample sizes. The vast majority of dates are not from sedimentary rocks. No. Yes, but not without the insertion being easily detectable. The effects of the heat, you know, and the shape of the insertion. I'm not sure, but perhaps.

The oldest known rocks (assemblages of minerals) are from the Slave Lake region of Canada, and are indeed just over 4 GA. Bowring, S. A. & Williams, I. S., 1999. Priscoan (4.00-4.03 Ga) orthogneisses from northwestern Canada, Contrib. Mineral. Petrol. v134 #1 pp 3-16; three rocks have ages of 4.0020.004 billion years (sample SAB91-63), 4.0120.006 billion years (sample SAB91-37), and 4.0310.003 billion years (sample SAB94-134). The Tera-Wasserberg concordia-discordia plot for sample SAB94-134 is at http://i2.photobucket.com/...10/JonF/SlaveLake_SAB94-134.png.The oldest known terrestrial minerals are zircons from Jack Hills in Australia, found in sedimentary rocks (so the rocks are not that old). Wilde SA, Valley JW, Peck WH and Graham CM (2001) Evidence from Detrital Zircons for the Existence of Continental Crust and Oceans on the Earth 4.4 Gyr Ago. Nature. 409: 175-178. The zircons are 4.4040.008 GA. Lots more on these zircons at Zircons Are Forever. Indeed the dates of many moon rocks and meteors are around 4.5 GA, and that is good evidence that the Earth is about that old. (See Part II. Radio-isotopic Dating; at the end are several tables of such ages reproduced from Dalrymple's "The Age of the Earth").But the 4.55 GA age of the Earth is derived from a lead-lead isochron analysis of almost solely terrestrial sources. Lead-lead isochrons are unlike other isochrons in that they are not "anchored"; the intercepts of the isochron line with the axes is meaningless, and you need to obtain an "anchor point" for the isochron line from something other than the lead content of your samples. We need to figure out the primordial lead isotope ratios of the Solar System; and that we get from the Canyon Diablo meteorite. This meteorite is primordial and contains essentially zero uranium (less than 10 ppb). So its current lead composition is also primordial to within a lot better than one percent. This anchors the isochron, and then terrestrial samples define the slope of the isochron, which determines the age; 4.55 billion years.There's a lot more to it than this; Dalrymple devotes an entire chapter to it, and that's not the really technical version. In particular, the primordiality of the Canyon Diablo meteorite has been checked many ways and passed all tests.

Probably not. Iron meteorites tend to have very small amounts of long-lived radioisotopes, and many of them cannot be dated. Apparently the Canyon Diablo meteorite is not a very extreme case. But it is the most extreme case we've found. Seems fair to me

I like paleosols. Loads of 'em in the Grand Staircase. Root traces. Soil horizons. Characteristic microstructures. Mmmmm-mmmm good.