welcome to class how do we determine the age of something?

Welcome to Class

How do we determine the age of something?

Agenda

• Radioactive Decay Lab

• Fossils Movie

• Fossils Notes

Radioactive Decay Lab

Movie

• Fill out the worksheet as you watch the movie

• I will be collecting these

FOSSILS

• fossils - trace or remains of organisms that lived long ago– discovered in sedimentary rock

• paleontology - scientific study of fossils

• Help find relative and absolute ages of rocks

Interpreting the Fossil Record

• Fossil Record – provides evidence about the history of life on Earth– Shows how organisms have changed over time

• Provide clues to past geologic events, climates, and the evolution of living things over time– see how environmental changes affected living

organisms

Interpreting the Fossil Record

• What do these giant fossilized oysters tell us?

Fossilization

• Dead organisms buried quickly or protected from decay become fossils

• Generally only the hard parts become fossils– Rarely an entire organism may be preserved

• Sometimes only a replica of the original organism remains– Others provide evidence that life once existed

Mummification

• Mummified remains are found in very dry places – most decay causing bacteria cannot survive in

these places

• Some ancient civilizations mummified their dead – extracted internal organs and wrapped the

body in strips of cloth

Amber• Insects get trapped in the sap and are

preserved when the sap hardens– Hardened tree sap is called amber

• Delicate features (legs/antennae/DNA) can be preserved

Tar Seeps

• When thick petroleum comes to Earth’s surface, it forms a tar seep– covered by water– Animals become trapped and preserved in the

tar

Freezing

• The low temperatures of frozen soil and ice can protect and preserve organisms – Most bacteria cannot survive freezing temps.,

organisms buried in frozen soil or ice do not decay

Petrification

• Mineral solutions (groundwater) replace original organic materials

• Some common petrifying minerals are silica, calcite, and pyrite.

• The substitution often results in the formation of a nearly perfect mineral replica of the original organism

Types of Fossils

Using a book, look up types of fossils

Include:– trace fossils– imprints– molds and casts– Coprolites– Gastroliths

Types of Fossils

• trace fossil - a fossilized mark that formed by the movement of an animal on or in soft sediment

• No part of the original organism survives in fossil form– fossilized evidence of past animal movement – provide information about prehistoric life

• A trace fossils in an important clue to the animal’s appearance and activities.

Imprints

• Carbonized imprints of leaves, stems, flowers, and fish made in soft mud or clay

• When original organic material partially decays, it leaves behind a carbon-rich film– An imprint displays the surface features of

the organism

Molds and Casts

• After a shell is buried, it decays and leaves an empty space called a mold– sand or mud fills a mold and hardens forming

a cast

• A cast is a replica of the original organism

Coprolites

• coprolites - fossilized dung or waste materials from animals

• They can be cut into thin sections and observed through a microscope. – See the feeding habits of animals, such as

dinosaurs

Gastroliths

• Some dinosaurs had stones in their stomachs to help grind their food– these stones, called gastroliths, survive as

fossils

• Gastroliths are recognized by smooth, polished surfaces and their close proximity to dinosaurs remains

Index Fossils• Index fossil - a fossil used to establish age

of rock layers– distinct, abundant, widespread – existed for only a short span of geologic time

• Help determine relative and absolute ages of rock layers

Index Fossils and Absolute Age

• Scientists can use index fossils to estimate absolute ages of specific rock layers

• Lived during short spans of geologic time, the layer where an index fossil was discovered can be dated accurately

• Scientists can also use index fossils to date rock layers in separate area