Question

Which are the remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically? A. trace fossils B. index fossils C. carbon films B. index fossils \(\quad\) D. body fossils

Short answer

The remains described are index fossils.

Step-by-step solution

Understanding Fossils

Fossils are the preserved remains or impressions of organisms that lived in the past. They help scientists understand the history of life on Earth.

Identifying the Key Characteristics

The question focuses on species remains that existed briefly, were abundant, and had a wide geographical distribution. These are important clues for determining the type of fossil.

Explaining Index Fossils

Index fossils are remains of species that lived for a short geologic time, were abundant, and were widespread. They are used by geologists to correlate the age of rock layers.

Reviewing Other Options

Trace fossils are indirect evidence of organisms (such as footprints), carbon films are thin layers of carbon residue, and body fossils are actual parts of the organism (bone, shell). None of these specifically match the criteria given in the question.

Key concepts

Fossils

Fossils are nature's way of archiving life from the past. Imagine these as time capsules, preserving tiny details of creatures that roamed the Earth millions of years ago. They are the remains or traces of plants and animals that once lived and provide a unique glimpse into the history and evolution of life. There are different types of fossils, such as:

• Body Fossils: These include preserved bones, teeth, and shells, representing the actual physical remains of an organism.
• Trace Fossils: These aren't the direct parts of any organism. Instead, they're indirect hints like footprints, burrows, or fecal matter which tell us about an organism's behavior.
• Index Fossils: These are highly significant as they help scientists determine the relative age of rock layers. Index fossils are widespread, short-lived species that act as markers for specific time periods.

By studying these fossils, researchers can piece together the environment, climate, and changes in ecosystems over time.

Geologic Time

Geologic time is a concept that helps us understand Earth's history across vast stretches of time. It is like a chronological calendar of Earth's past, organized into different segments to mark important events in Earth's history.

• Eons are the largest time units, covering billions of years.
• Eras, smaller than eons, are further divided and known for significant events, like the extinction of dinosaurs.
• Periods and Epochs are smaller divisions that allow scientists to pinpoint more specific events during shorter time spans.

Geologists use tools like index fossils to determine the age of rock layers, keeping track of changes over time. Understanding geologic time helps scientists to date rocks and fossils accurately, revealing the timeline of Earth's development.

Rock Layers

Rock layers, often called strata, can be seen as pages in a history book telling the story of Earth's past. These layers stack upon each other over millions of years, each containing valuable information about the environment and life forms during that period.

• Formation: Different sediments like sand, silt, and clay settle over time, compressing into solid layers.
• Stratigraphy: The study of these layers visually and scientifically to understand Earth's history and the relative age of each layer. It's like reading a timeline, where deeper layers are older and the top layers are younger.
• Uniformitarianism: This principle states that the processes we observe today were the same in the past, helping to understand geological changes.

Index fossils within these rock layers help correlate and date the layers globally. By analyzing rock layers, scientists can uncover the chronological story of Earth's geologic and biological evolution.