11. He later worked on similar jobs across the length and breadth of England all the while studying the newly revealed strata and collecting all the fossils he could find．
12. But as more and more accumulations of strata were cataloged in more and more places, it became clear that the sequences of rocks sometimes differed from region to region and that no rock type was ever going to become a reliable time marker throughout the world.
13. Quartz is quartz—a silicon ion surrounded by four oxygen ions— there’s no difference at all between two-million-year-old Pleistocene quartz and Cambrian quartz created over 500 million years ago．
14. As he collected fossils from strata throughout England, Smith began to see that the fossils told a different story from the rocks particularly in the younger strata the rocks were often so similar that he had trouble distinguishing the strata, but he never had trouble telling the fossils apart.
15. While rock between two consistent strata might in one place be shale and in sandstone, the fossils in that shale or sandstone were always the same.
16. Some fossils endured through so many millions of years that they appear in many strata, but others occur only in a few strata, and a few species had their births and extinctions within one particular stratum.
17. By following the fossils, Smith was able to put all the strata of England's earth into relative temporal sequence.
18. Limestone may be found in the Cambrian or-300 million years later-in the Jurassic strata but a trilobite—the ubiquitous marine arthropod that had its birth in the Cambrian—will never be found in Jurassic strata, nor a dinosaur in the Cambrian.
19. The sheer passage of time does not account for it; adults have excellent recognition of pictures of people who attended high school with them 35 years earlier.
20. Children two and a half to three years old remember experiences that occurred in their first year, and eleven month older than them can remember some events a year later.
