Index Fossils

Front

Index Fossil Noun

---

[in-deks fos-uhl]

Back

Index Fossil

---

A fossil of a widely distributed organism that lived for a short geologic time, used to date rock layers.

---

Example: This diagram shows rock layers with different fossils. The 'index fossil' is ideal for dating layers because it existed for only a short time.

Front

Fossil Noun

---

[fos-uhl]

Back

Fossil

---

The preserved remains or traces of an organism from a past geological age, typically found embedded within rock layers.

---

Example: This diagram shows how specific fossils, called index fossils, are used to match the age of rock layers (strata) in different locations (A and B).

Front

Absolute Dating Noun

---

[ab-suh-loot dey-ting]

Back

Absolute Dating

---

A method used to determine the actual numerical age of a rock or fossil, often expressed in years.

---

Example: This diagram shows rock layers with index fossils being assigned specific numerical ages, such as "400 million years ago," which is the definition of absolute dating.

Front

Relative Age Noun

---

[rel-uh-tiv eyj]

Back

Relative Age

---

The age of a rock or fossil determined by comparing its position to other rocks or fossils in sequence.

---

Example: This diagram shows how to find the relative age of rock layers. Older layers (E) are at the bottom, and younger layers (A) are on top.

Front

Correlation Noun

---

[kawr-uh-ley-shuhn]

Back

Correlation

---

The process of matching rock layers or fossils from different geographic locations to establish if they are the same age.

---

Example: This diagram shows how geologists match up rock layers (strata) from different locations. This process, called correlation, helps prove the layers are the same age.

Front

Outcrop Noun

---

[out-krop]

Back

Outcrop

---

A visible exposure of bedrock or ancient superficial deposits on the surface of the Earth, revealing underlying rock layers.

---

Example: This diagram shows a cross-section of the Earth where folded rock layers (strata) are exposed at the surface, forming an outcrop.

Front

Geologic Cross Section Noun

---

[jee-uh-loj-ik kros sek-shuhn]

Back

Geologic Cross Section

---

A diagram that illustrates a vertical slice of the Earth's crust, showing the arrangement and sequence of rock layers.

---

Example: This diagram shows a geologic cross-section, a side view of rock layers (strata). It reveals the relative positions of different rock layers and geologic features.

Front

Extinct Adjective

---

[ik-stingkt]

Back

Extinct

---

A term describing a species of organism that no longer has any living members anywhere in the world.

---

Example: The dodo is a well-known bird that is now extinct, meaning the entire species has died out and no longer exists on Earth.

Front

Carbon Dating Noun

---

[kahr-buhn dey-ting]

Back

Carbon Dating

---

A specific method of absolute dating that measures the decay of carbon-14 to determine the age of organic materials.

---

Example: This graph shows that after each 'half-life,' the amount of a radioactive substance decreases by half, which is the principle behind carbon dating fossils.