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. Humanlike ancestors (hominids) have been around for roughly 5 million years. What percentage of geologic time is represented by the existence of 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

Understand the Problem

We need to express various time durations as a percentage of Earth's age, which we are rounding to 5 billion years. Specifically, we'll calculate the percentage for recorded history (5000 years), the existence of hominids (5 million years), and the time since the Cambrian period (540 million years).

Calculate the Percentage for Recorded History

To find the percentage, divide the duration of recorded history by Earth's age and multiply by 100:\[ \text{Percentage of recorded history} = \left( \frac{5000}{5,000,000,000} \right) \times 100 \]\[ \text{Percentage of recorded history} = 0.0001\% \]

Calculate the Percentage for Hominids

Divide the duration of humanlike ancestors by Earth's age and multiply by 100:\[ \text{Percentage of hominids} = \left( \frac{5,000,000}{5,000,000,000} \right) \times 100 \]\[ \text{Percentage of hominids} = 0.1\% \]

Calculate the Percentage for Abundant Fossil Evidence

Divide the duration since the Cambrian period by Earth's age and multiply by 100:\[ \text{Percentage of fossil evidence} = \left( \frac{540,000,000}{5,000,000,000} \right) \times 100 \]\[ \text{Percentage of fossil evidence} = 10.8\% \]

Concluding the Calculations

Through the calculations, we found that recorded history constitutes 0.0001% of Earth's history, hominids exist for 0.1% of Earth's history, and abundant fossils cover 10.8%.

Key concepts

Geologic Time

Geologic time is an enormous timescale that researchers use to better understand the history and development of Earth. It helps frame the age of the Earth which spans about 4.5 billion years. To simplify calculations, we often round this up to 5 billion years. This timeline is so vast that it can be challenging to comprehend.
To break it down, scientists have divided geologic time into several hierarchical segments called eons, eras, periods, epochs, and ages. Each segment stands for a significant chapter in Earth's history.

• Eon: The largest time unit, covering billions of years.
• Era: Subdivisions of eons, each lasting hundreds of millions of years.
• Period: Divisions of eras, often tens of millions of years long.
• Epoch: Smaller divisions within periods, typically lasting millions of years.

This systemic breakdown allows us to pinpoint major events such as the emergence of significant life forms, mass extinctions, and tectonic shifts.

Recorded History

Recorded history refers to the era of human history that has been documented in some form. It spans roughly 5000 years and marks the time when human beings began keeping written records. Compared to Earth's 5 billion year history, this duration is minuscule.
Despite its brevity, recorded history is significant because it provides direct insights into the evolution of human societies. It covers major developments in culture, philosophy, politics, and technology. Key historical periods within recorded history include:

• Ancient Civilization: Including Mesopotamia, Ancient Egypt, and the Indus Valley.
• Classical Antiquity: Encompassing the Greek and Roman empires.
• Middle Ages: Also known as the Medieval Period.
• Modern Era: Includes the Renaissance through to contemporary times.

Understanding recorded history allows us to trace humanity's progress and its impact on the world.

Cambrian Period

The Cambrian Period, which began around 540 million years ago, marks a critical chapter in Earth's geologic history. It is renowned for the "Cambrian Explosion," a remarkable event during which most major groups of animals first appeared in the fossil record. This period saw a rapid increase in the diversity of complex life forms.
During the Cambrian, Earth's environmental conditions favored the emergence and flourishing of new species, with marine life forms dominating the scene. Trilobites, brachiopods, mollusks, and the ancestors of modern-day vertebrates were abundant.
The Cambrian Period was just the beginning, setting the stage for future biodiversity that evolved over millions of years. In the grand timeline of Earth's 5 billion-year history, the Cambrian Period occupies a significant role, contributing to around 10.8% of the time span we consider significant for the emergence of abundant fossil evidence.

Hominids

Hominids, also known as human-like ancestors or our ancient relatives, have been part of Earth's history for about 5 million years. This group includes modern humans, extinct species, and all our ancestors that have descended from a common ape-like ancestor.
Hominids are significant for understanding human evolution, as they provide insights into our origins and adaptations. Some key characteristics that distinguish hominids are upright walking (bipedalism), larger brain sizes, and the ability to use tools.
Despite the richness of hominid evolution, they account for just 0.1% of Earth's total 5 billion-year history. Here are some well-known members of the hominid family:

• Australopithecus: One of the earliest human ancestors, famed for the "Lucy" fossil.
• Homo habilis: Known as "handy man," for its association with early stone tools.
• Homo erectus: Among the first to use fire and migrate out of Africa.
• Homo sapiens: Our species, characterized by advanced cognitive abilities.

Studying hominids is essential to grasp the complexities of human ancestry and evolutionary development.