Question

Solve the problems related to the magnitude of Earth history below. 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. Humanlike ancestors (hominids) have been around for roughly 5 million years. What percentage of geologic time is represented by these 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

Understanding the Problem

We need to compare different periods of time with the entire history of Earth, which we will assume to be 5 billion years. For each part of the question, we will find what percentage of Earth's total age is represented by the different times mentioned. The formula for percentage is \( \text{Percentage} = \left( \frac{\text{part}}{\text{total}} \right) \times 100 \).

Solve for Recorded History Percentage

The length of recorded history is 5000 years. To find the percentage it represents of Earth's 5 billion years, we apply the formula: \[ \text{Percentage of Recorded History} = \left( \frac{5000}{5,000,000,000} \right) \times 100 \]. Calculate the fraction: \( \frac{5000}{5 \times 10^9} \) equals \( 10^{-6} \), and multiplying by 100 gives: \( 10^{-4} \) or 0.0001%.

Solve for Hominids' Time Percentage

Hominids have been around for 5 million years. Using the percentage formula: \[ \text{Percentage for Hominids} = \left( \frac{5,000,000}{5,000,000,000} \right) \times 100 \]. Simplifying the fraction gives \( \frac{1}{1000} \), which equals 0.1% when multiplied by 100.

Solve for Abundant Fossil Evidence Percentage

First abundant fossil evidence appeared 540 million years ago. Using our formula again: \[ \text{Percentage of Abundant Fossil Evidence} = \left( \frac{540,000,000}{5,000,000,000} \right) \times 100 \]. This simplifies to \( \frac{108}{1000} \) which gives 10.8% when multiplied by 100.

Key concepts

Recorded History Percentage

When we talk about Earth's geological time, the scope of its vast history is almost unimaginable. Recorded history, which captures everything humans have documented, spans approximately 5000 years. But what does this mean in the context of Earth's age of about 5 billion years? Let's break this down:

• Recorded history is a mere blink in the scale of geologic time.
• To understand this minuscule span, we calculate the percentage it represents using the formula for percentage: \( \text{Percentage} = \left( \frac{\text{part}}{\text{total}} \right) \times 100 \).

So, for recorded history: \[ \text{Percentage of Recorded History} = \left( \frac{5000}{5,000,000,000} \right) \times 100 \].This results in a tiny 0.0001%, underscoring the fleeting nature of recorded human presence on Earth in the grand tapestry of time.

Hominid Timeline

Hominids, or our humanlike ancestors, have walked the Earth for about 5 million years. In comparison to recorded history, this seems lengthy, but how significant is it in relation to Earth's 5 billion-year history?By calculating the percentage of geological time occupied by hominids, using the formula: \[ \text{Percentage for Hominids} = \left( \frac{5,000,000}{5,000,000,000} \right) \times 100 \].This calculation reveals that hominids represent 0.1% of Earth's age. This percentage makes one appreciate the relatively recent emergence of hominid species and their short reign compared to the planet's extensive past.

Cambrian Period

The Cambrian period is a fascinating era in Earth’s history, marking the explosion of abundant fossils found around 540 million years ago. But how does this milestone fit into the full timeline of Earth?To connect this period to Earth's entire history, we use: \[ \text{Percentage of Abundant Fossil Evidence} = \left( \frac{540,000,000}{5,000,000,000} \right) \times 100 \].The calculation shows the Cambrian period accounts for 10.8% of Earth's geological history. This relatively significant span emphasizes the dominance of life forms documented since then and how the Cambrian period was crucial for the diversification of life that would lead to the planet we know today.