You should see a white crescent called the lunula. The cuticle is the piece of skin that overlaps the hard nail and touches the lunula. You may be wondering what they do, or why you need them. If you get frequent manicures, they may be smooth and even, pushed back as far as they'll go.If not, they may be ragged and torn, or creeping up on the nail.he cuticle is the piece of skin that overlaps the hard nail and touches the lunula. You may be wondering what they do, or why you need them. If you get frequent manicures, they may be smooth and even, pushed back as far as they'll go.
Index fossils. Radiometric dating. The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly. Scientists use two kinds of dating techniques to work out the age of rocks and fossils. The first method is called relative dating.
Two isotopes of uranium are used for radiometric dating. Uranium-238 decays to form lead-206 with a half-life of 4.47 billion years. Uranium-235 decays to form lead-207 with a half-life of 704 million years. Uranium-lead dating is usually performed on crystals of the mineral zircon (Figure 11.26).