Chapter 9, Section 1: Relative Dating Ahhh! I’m not dating HER ! She’s my cousin! Eewww! No way!
9.1 The beginnings of geology • In 1666, Nicholas Steno, a Danish anatomist, studied a shark’s head and noticed that the shark’s teeth resembled mysterious stones called “tonguestones”.
9.1 Evidence from Rock • Steno theorized that tonguestones looked like shark’s teeth because they actually were shark’s teeth that had been buried and became fossils.
What is relative dating? • Steno’s principles are used by geologists to determine the age of fossils and rocks in a process called relative dating. • Relative dating is a method of sequencing eventsin the order they happened. Use relative dating to determine which event – the foot step, the tire track, or the snow fall - happened first.
The Present Explains the Past • James Hutton (1726–1797) showed how processes today might explain what happened a long time ago. • For example, when it rains really hard you might see flowing water washing away sediment. When the rain stops, you might see grooves left behind by the flowing water.
Superposition • Steno’s ideas for relative dating include superposition, original horizontality, and lateral continuity. • Superposition states that the bottom layer of sedimentary rock is older than the layer on top because the bottom layer formed first. A stack of newspapers illustrates superposition. The oldest newspaper is on the bottom of the stack and the more recent newspapers are piled on, with the most recent on top.
The Fossil Record The fossil record is the ordering of fossils throughout geological time in layers of rock that accumulate and form.
Faunal Succession • Faunal successionuses fossils to identify the relative age of the layers of a rock formation. • The organisms found in the top layers appeared after the organisms found in the layers below them. Use the illustration (above) to answer the following questions: Did human beings live at the same time as the dinosaurs? Did dinosaurs roam the earth at the same time as trilobites?
Fossils and Earth’s changing surface • Most of the land on Earth was part of a large landmass, called Pangaea, about 250 million years ago.
● Fossils provide evidence for how Earth’s surface has changed over time.● Scientists map fossil locations.● Understanding Earth’s past helps explain how similar plants and animals ended up in different locations.
Huh? Did you know….that shark teeth are common fossils in Georgia and are the official state fossil? From the Cretaceous to the Miocene periods (approximately 10 to 70 million years ago) sharks hunted and stalked the coastal areas of Georgia. It is very rare to find a fossil of an actual carcass of these prehistoric sharks, but their teeth are found in sizable numbers due to the fact that sharks constantly lose and replace their teeth.