Radiometric dating has determined that earth is approximately
Correlation determines if rocks are the same age, and is a key tool that geologists use to identify the relative ages of rocks where a rock layer is not continuously exposed.It is also how geologists relate rocks from one region to another.The Principle of Superposition and the Principle of Original Horizontality [see Photo 4] (sedimentary rocks are always deposited flat, i.e., horizontally) allow geologists to reconstruct the sequence of events.Cross cutting relationships [see Photo 5] also demonstrate relative ages because what does the cutting (whether it is a fault or a dike) must be younger than what is cut.Both techniques are important in different geologic situations.
No rock layers contain both trilobites and dinosaurs (or dinosaurs and humans), so these distinctions can be very clear.The Grand Canyon landscape is geologically young, being carved within just the last 6 m.y.There are younger geologic deposits in Grand Canyon too, such as the Ice Age fossils found in caves, a 1000-year-old lava flow in the western canyon, and even the debris flow deposits that continue form each year.Rock type (or lithology) is usually not a good basis for correlation.Some rock types look much the same regardless of their age (the 275 m.y.
Search for radiometric dating has determined that earth is approximately:
Grand Canyon National Park [see Photo 1] is one of the best places in the world to gain a sense of geologic, or “deep,” time because the canyon exposes a great swath of geologic history.