Question

Solve the problems below. To make calculations easier, round the age of Earth to 5 billion years. a. What percentage of geologic time is represented by recorded history? (Assume 5,000 years for the length of recorded history.) b. Human-like ancestors (hominids) have been around for roughly 5 million years. What percentage of geologic time is represented by the existence of the ancestors? c. The first abundant fossil evidence does not appear until the beginning of the Cambrian period, about 540 million years ago. What percentage of geologic time is represented by abundant fossil evidence?

Short answer

a) 0.0001% b) 0.1% c) 10.8%

Step-by-step solution

Understand the Problem Statement

We need to calculate the percentage of Earth's geological time for different events: recorded history, the existence of hominids, and the first abundant fossils. We will use Earth's age as approximately 5 billion years, with one billion equal to a thousand million.

Calculate Percentage of Recorded History

Recorded history = 5,000 years. Earth's age = 5 billion years = 5,000,000,000 years. Percentage for recorded history = \( \frac{5,000}{5,000,000,000} \times 100 \).

Perform Calculation for Recorded History

Solving \( \frac{5,000}{5,000,000,000} \times 100 \) gives:\[ \frac{5,000}{5,000,000,000} = 0.000001 \]\( 0.000001 \times 100 = 0.0001\% \).

Calculate Percentage for Existence of Hominids

Hominids' existence = 5 million years. Earth's age = 5,000 million years. Percentage for hominids = \( \frac{5,000,000}{5,000,000,000} \times 100 \).

Perform Calculation for Hominids

Solving \( \frac{5,000,000}{5,000,000,000} \times 100 \) gives:\[ \frac{5,000,000}{5,000,000,000} = 0.001 \]\( 0.001 \times 100 = 0.1\% \).

Calculate Percentage for Abundant Fossil Evidence

Fossil evidence starting from Cambrian = 540 million years ago. Earth's age = 5,000 million years. Percentage for fossil evidence = \( \frac{540,000,000}{5,000,000,000} \times 100 \).

Perform Calculation for Fossil Evidence

Solving \( \frac{540,000,000}{5,000,000,000} \times 100 \) gives:\[ \frac{540,000,000}{5,000,000,000} = 0.108 \]\( 0.108 \times 100 = 10.8\% \).

Key concepts

Recorded History

Recorded history refers to the span of time for which there is documented evidence of human activities and events. This began approximately 5,000 years ago with the advent of writing in ancient civilizations such as those in Mesopotamia and Egypt. Compared to the age of the Earth, which is about 5 billion years, recorded history occupies an incredibly small fraction. When calculating this proportion, it amounts to only a tiny 0.0001% of Earth's geologic time. In the grand scheme of things, recorded history is a mere blink, emphasized further by the vast stretches of time that predate written documentation. Understanding this tiny percentage helps us appreciate the magnitude and depth of Earth's past, most of which is not captured by written records. It is thanks to other forms of evidence, like fossils and geological formations, that we have a glimpse into the prehistorical world.

Hominids

Hominids, also known as the great apes, include humans as well as our closest evolutionary relatives. The existence of hominids on Earth spans nearly 5 million years, which is slightly more significant in the context of Earth's grand timeline than recorded history. This accounts for about 0.1% of Earth's geological age. Hominids developed complex tools, social structures, and eventually advanced communication methods, leading to Homo sapiens. The study of hominids is crucial for understanding human evolution. Fossils and archaeological findings offer insights into their way of life, adaptation strategies, and migration patterns, painting a vivid picture of our ancestors' journey.

Cambrian Period

The Cambrian Period marks a significant phase in Earth's history, starting around 540 million years ago. It is often referred to as a "biological explosion" due to the rapid emergence of a diverse array of life forms. This period represents around 10.8% of the geologic time scale, making it a substantial chapter in Earth's story. During the Cambrian, many marine animals developed hard shells, which improved fossilization. This hard shell development is why we have a rich fossil record from this era. The Cambrian Period laid the foundation for complex life, evolving into the diverse ecosystems seen today.

Fossil Evidence

Fossil evidence is crucial for piecing together Earth's ancient history, providing windows into the lives of creatures long extinct. Fossils are remains or traces of ancient organisms, often trapped within rock layers formed during specific geological periods. The first abundant fossil evidence dates to the Cambrian period, marking a fascinating chapter in Earth's biological history. Fossils help us identify when certain life forms appeared, diversified, or became extinct, forming a timeline of evolution. Paleontologists, scientists who study fossils, use these evidences to learn about past climates, habitats, and biological changes. The study of fossils continues to reveal new information about the Earth, its life, and the processes that shaped its current state.