The Fossil Record

Front

Extinct Adjective

---

[ik-stingkt]

Back

Extinct

---

A term used to describe a species that has died out completely and no longer exists anywhere on Earth.

---

Example: This image shows a woolly mammoth, an animal that no longer exists, to explain the concept of extinction. The extinction date reinforces its status.

Front

Paleontologist Noun

---

[pay-lee-un-tahl-uh-jist]

Back

Paleontologist

---

A researcher who studies the history of life on Earth through the examination of the fossil record.

---

Example: This image shows a paleontologist, a scientist who studies fossils, carefully using a brush to clean a large fossil bone at an excavation site.

Front

Fossil Record Noun

---

[fos-uhl rek-erd]

Back

Fossil Record

---

The history of life as documented by fossils, which provides information about ancient organisms and their evolutionary history.

---

Example: This diagram shows fossils in different rock layers, with older fossils like coral found in deeper layers and younger fossils like ferns in shallower layers.

Front

Trace Fossil Noun

---

[treys fos-uhl]

Back

Trace Fossil

---

A type of fossil that provides indirect evidence of an organism's activities, such as footprints, burrows, or droppings.

---

Example: This diagram shows how a trace fossil, like a dinosaur footprint, is formed when an impression in mud is filled with sediment, creating a mold and cast.

Front

Sedimentary Rock Noun

---

[sed-uh-men-tuh-ree rok]

Back

Sedimentary Rock

---

A type of rock formed from the accumulation of small particles like sand or clay, where most fossils are preserved.

---

Example: This diagram shows that sedimentary rocks are formed in layers, and older layers with older fossils are found underneath younger layers with more recent fossils.

Front

Relative Dating Noun

---

[rel-uh-tiv dey-ting]

Back

Relative Dating

---

A method of determining the age of a fossil by comparing its placement with that of fossils in other layers.

---

Example: This diagram shows that deeper rock layers (C) are older than shallower layers (A), and features that cut through layers (D, E) are the youngest.

Front

Index Fossil Noun

---

[in-deks fos-uhl]

Back

Index Fossil

---

A distinctive fossil used to establish and compare the relative ages of rock layers and the fossils they contain.

---

Example: This diagram shows that specific fossils, like trilobites and ammonites, are found only in certain rock layers corresponding to specific geologic time periods.

Front

Radiometric Dating Noun

---

[rey-dee-oh-me-trik dey-ting]

Back

Radiometric Dating

---

A method for determining the absolute age of a sample by using the proportion of radioactive to stable isotopes.

---

Example: This graph shows that after each 'half-life,' the amount of a radioactive substance decreases by 50%, a predictable decay used to date fossils.

Front

Half-life Noun

---

[haf-lahyf]

Back

Half-life

---

The time required for half of the radioactive atoms in a given sample to decay into more stable forms.

---

Example: As igneous rock forms, radioactive parent atoms get trapped. Over one half-life, half of these atoms decay into stable daughter atoms, a process used to date rocks.

Front

Geologic Time Scale Noun

---

[jee-uh-loj-ik tahym skeyl]

Back

Geologic Time Scale

---

A timeline of Earth's history based on relative and absolute dating, divided into eons, eras, and periods.

---

Example: This chart organizes Earth's history into units like eons, eras, and periods, showing the sequence from oldest (bottom) to youngest (top).