The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brogniart in the early 19th century, enabled geologists to divide Earth history more precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies between 1820 and 1850 of the strata and fossils of Europe produced the sequence of geological periods still used today... [No million year dates]
...When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, time scales could be estimated only very imprecisely since various kinds of rates of change used in estimation were highly variable... [again no dates]
...While creationists had been proposing dates of around six or seven thousand years for the age of the Earth based on the Bible, early geologists were suggesting millions of years for geologic periods with some even suggesting a virtually infinite age for the Earth. Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification.[no dates for eras]
http://en.wikipedia.org/wiki/Geologic_t ... _and_names
Holmes was a pioneer of geochronology, and performed the first uranium-lead radiometric dating (specifically designed to measure the age of a rock) while an undergraduate at the Royal College of Science (now Imperial College) in London, assigning an age of 370 Ma to a Devonian rock from Norway.... [no information as to how he estimated ages]
...1912 saw Holmes on the staff of Imperial College, publishing his famous booklet The Age of the Earth in 1913 ( he estimated the Earth's age to be 1,600 Ma)...[no information as to how he did this]
http://en.wikipedia.org/wiki/Arthur_Holmes
Before long, scientific inquiries provoked by his claims had pushed back the age of the earth into the millions of years – still too short when compared with the accepted 4.6 billion year age in the 21st century, but a distinct improvement. [still no mention of how geological timescales were derived?]
http://en.wikipedia.org/wiki/James_Hutton
Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloguing and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand however, to the point they share the same system of naming rock layers and the time spans utilized to classify layers within a strata.
[this is saying exactly what Richard Milton said in my earier quote]
http://en.wikipedia.org/wiki/Geochronology