Reality → Life → Evolution → Verification
Many scientific branches come together to solve the puzzle of when and how developments happened that are forever gone and often left only scant evidence or, mostly, no traces at all. Though the painstaking work often yields inaccurate or debated results, the overall picture is undisputed among scientists, due to evidence gained from:
Stratigraphical and structural analysis of fossil-bearing sedimentary rocks in different parts of the world reveals the timely sequence of evolutionary events (see Note 2 for an example of the close link between paleontology and geology).
Radiometric dating allows the absolute dating of rocks (see also decay and Isotopes, Note 4). One of the most common methods is the measurement of the decay of uranium to lead by mass spectrometry. Error margins of less then 5% can be achieved for rocks as old as 2 billion years. As the method is restricted to igneous and metamorphic rocks, the approximate age of fossil-bearing sediments can be deduced from the age of over- and underlying rocks.
Modern (molecular) genetics, insights into cell division and differentiation, and the concept of the molecular clock identify new evolutionary relationships and clades (whose age estimates vary widely with assumed mutation rates and require calibration with fossil evidence and radiometric dating).