Question

Solve the problems below that relate to the magnitude of Earth history. To make calculations easier, round Earth's age to 5 billion years. a. What percentage of geologic time is represented by recorded history? (Assume 5000 years for the length of recorded history.) b. Humans and their close relatives (hominins) have been around for roughly 5 million years. What percentage of geologic time is represented by the history of this group? 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

0.0001%, 0.1%, and 10.8% for recorded history, hominins, and Cambrian period, respectively.

Step-by-step solution

Understand the problem parameters

We need to calculate the percentage of Earth's history represented by three distinct periods: recorded history, human existence, and the Cambrian period. Earth's age is approximated as 5 billion years (or 5,000,000,000 years).

Record the given timeframes

We have: - Recorded history = 5000 years - Hominins history = 5 million years = 5,000,000 years - Abundant fossil evidence from the Cambrian period = 540 million years = 540,000,000 years

Calculate percentage for recorded history

For recorded history the percentage is calculated by the formula:\[\text{Percentage} = \left( \frac{\text{Recorded history}}{\text{Total Earth's Age}} \right) \times 100\]Substitute the values:\[\text{Percentage} = \left( \frac{5000}{5,000,000,000} \right) \times 100 = 1 \times 10^{-4} \%\]

Calculate percentage for hominins history

For the history of hominins:\[\text{Percentage} = \left( \frac{\text{Hominins history}}{\text{Total Earth's Age}} \right) \times 100\]Substitute the values:\[\text{Percentage} = \left( \frac{5,000,000}{5,000,000,000} \right) \times 100 = 0.1 \%\]

Calculate percentage for Cambrian fossil evidence

For the Cambrian fossil evidence:\[\text{Percentage} = \left( \frac{\text{Cambrian evidence period}}{\text{Total Earth's Age}} \right) \times 100\]Substitute the values:\[\text{Percentage} = \left( \frac{540,000,000}{5,000,000,000} \right) \times 100 = 10.8 \%\]

Conclusion

The percentages representing each period of Earth's history are: - Recorded history: 0.0001% - Hominins history: 0.1% - Cambrian fossil evidence: 10.8%

Key concepts

Earth's History

When we discuss Earth's history, we're talking about an incredibly long timeline stretching back approximately 5 billion years. This vast span of time includes the planet's formation, the development of its atmosphere, the origin of life, and numerous geological and biological changes. In order to better comprehend such an extensive duration, scientists divide Earth's history into distinct time frames.

• These divisions help in structuring geological and biological phenomena.
• Major events mark the transitions between these divisions, such as mass extinctions and significant climate changes.

By examining Earth's past, scientists gain insights into the formation and development processes of planets in our solar system and beyond. Each phase of Earth's history sheds light on different evolutionary stages, from single-celled organisms to complex life forms.

Hominins

Hominins are a group of species that include modern humans and our closest evolutionary ancestors. They have been around for approximately 5 million years. This period is just a tiny fraction of Earth's entire history, as calculated to be about 0.1%.

• Hominins are characterized by bipedal locomotion, meaning they walk on two legs.
• Their evolution showcases gradual advancements, such as increased brain size and the use of tools.

Understanding the history of hominins gives us valuable insights into human evolution and adaptation. These adaptations were crucial for survival in various environments and shaped the development of human societies today.

Cambrian Period

The Cambrian Period, beginning around 540 million years ago, marks a significant chapter in Earth's history known for the 'Cambrian Explosion'—a rapid increase in the diversity of life forms. Prior to this, fossil evidence is scarce, but during this period, many new marine organisms emerged.

• The Cambrian Explosion is notable for the rise of most major animal phyla.
• It represents about 10.8% of Earth’s history, which is significant compared to other events like the appearance of hominins.

The abundance of fossil evidence from this period allows scientists to study past ecosystems and understand the evolutionary pathways that led to the complex life forms existing today. This period was vital for setting the foundation for future biodiversity.

Recorded History

Compared to the entire span of Earth's history, recorded history covers an incredibly brief amount of time, approximately 5000 years, amounting to a negligible 0.0001% of geological time.

• Recorded history relies on written, visual, and oral records preserved over generations.
• These records provide crucial insights into human societies, cultures, and technological advancements.

Even though recorded history is minute in the grand timeline, it holds immense importance as it documents human civilizations, events, and innovations from ancient times to the present. By studying recorded history, we better understand our past and how it influences our present and future world.