Vocabulary Words!!!!
Fossil - the remains or physical evidence of an organism preserved by geological processes
Trace fossil - a fossilized mark that is formed in soft sediment by the movement of an animal
Mold - a mark or cavity made in a sedimentary surface by a shell or other body
Cast - a type of fossil that forms when sediments fill in the cavity left by a decomposed organism
Index fossil - a fossil that is found in the rock layers of only one geologic age and that is used to establish the age of the rock layers
Trace fossil - a fossilized mark that is formed in soft sediment by the movement of an animal
Mold - a mark or cavity made in a sedimentary surface by a shell or other body
Cast - a type of fossil that forms when sediments fill in the cavity left by a decomposed organism
Index fossil - a fossil that is found in the rock layers of only one geologic age and that is used to establish the age of the rock layers
Relative Dating
Geologists use relative dating to determine the order in which events happen. Determining whether an object or event is older or younger than other objects or events is called relative dating.
Radioactive Decay
To determine the absolute ages of fossils and rocks, scientists analyze isotopes of radioactive elements. Atoms of the same element that have the same number of protons but have different numbers of neutrons are called isotopes. Most isotopes are stable meaning that they stay in their original form. But some isotopes are unstable. Scientists call unstable isotopes radioactive. Radioactive isotopes tend to break down into stable isotopes of the same or other elements in a process called radioactive decay.
Radiometric Dating
If you know the rate of decay for a radioactive element in a rock, you can figure out the absolute age of the rock. Determining the absolute age of a sample, based on the ratio of parent material to daughter material is called radiometric dating. Radiometric dating is a method of determining the age of an object by estimating the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.