The Changing Earth

Understanding Earth Absolute dating - is the process of determining an approximate computed age in archaeology and geology. provides a computed numerical age

Radioactive Dating All rocks and minerals contain tiny amounts of radioactive elements Unstable Radioactive elements break down into stable elements over time The radioactive element is called the parent The stable new element is called the daughter.

Radioactive Dating Half-life – the time it takes for half of the atoms of a parent element to change into atoms of the daughter element. radium-226, which has a half-life of 1,622 years ? What happens to 10 grams of radium after 1,622 years? A. Five grams of radium remain, and five grams will have changed into lead.

Understanding Earth Geology is the study of rocks and materials that make up Earth and the processes that shape it. In 1666, Nicholas Steno ( ) noticed that shark’s teeth resembled mysterious stones called “tonguestones” that were found in local rocks.

Understanding Earth Steno’s explanation helped him develop ideas about how rocks and fossils form. These ideas are used in a technique called relative dating. Relative dating is a way to put events in the order in which they happened. What happened here and in what order?

Understanding Earth The approximate age of each layer of a rock formation can be determined by applying Steno’s idea called superposition. A stack of newspapers illustrates superposition. Superposition means that the bottom layers of rock are older than the layers on the top.

Understanding Earth Original horizontality states that sediment particles fall to the bottom of a basin, such as a riverbed, in response to gravity and result in horizontal layers.

Understanding Earth Lateral continuity is the idea that layers of sediment extend in all directions when they form and before they become rock layers. The idea of lateral continuity states that layers of rock are continuous unless a geologic event like a river interrupts the layers or an earthquake them.

Understanding Earth Another important idea, developed by Scottish geologist James Hutton ( ), is that the "present explains the past." The idea of cross- cutting relationships states that a vein of rock is younger than the rock that surrounds a vein. vein

Understanding Earth Sometimes rock pieces called inclusions are contained in another rock. During the formation of a rock with inclusions, sediments or melted rock surrounded the inclusion and then solidified. Therefore, the inclusions are older than the surrounding rock.

Understanding Earth Over geologic history, many animals and plants have lived and become extinct. Their remains have become fossils. The idea of faunal succession states that fossils can be used to identify the relative age of layers of a rock formation.