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 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

Calculate Earth's Age in Years

To solve these problems, we first need to work in the same unit of time, which is years. It is given that Earth's age is approximately 5 billion years. To express this in terms of years, convert billion to numerical form: \[ 5 \text{ billion years} = 5 \times 10^9 \text{ years} \]

Calculate Percentage for Recorded History

Recorded history is approximately 5000 years. The percentage of Earth's history this represents is calculated by dividing the time span of recorded history by Earth's total age and then multiplying by 100 to convert it into a percentage: \[ \text{Percentage} = \left( \frac{5000 \text{ years}}{5 \times 10^9 \text{ years}} \right) \times 100 \]Calculate this value to find the percentage.

Solution for Recorded History

Plug the numbers into the formula from Step 2:\[ \text{Percentage} = \left( \frac{5000}{5 \times 10^9} \right) \times 100 = 0.0001\% \]So, recorded history represents 0.0001% of Earth's history.

Calculate Percentage for Hominids

Hominids have been around for roughly 5 million years. We calculate the percentage of Earth's history this represents using a similar approach: \[ \text{Percentage} = \left( \frac{5 \times 10^6 \text{ years}}{5 \times 10^9 \text{ years}} \right) \times 100 \]This will give us the percentage of Earth's history represented by hominids.

Solution for Hominids

Plug the numbers into the formula from Step 4:\[ \text{Percentage} = \left( \frac{5 \times 10^6}{5 \times 10^9} \right) \times 100 = 0.1\% \]Hominids have existed for about 0.1% of Earth's history.

Calculate Percentage for Abundant Fossil Evidence

The first abundant fossil evidence dates back to the Cambrian period, about 540 million years ago. We'll calculate the percentage of Earth's history this represents: \[ \text{Percentage} = \left( \frac{540 \times 10^6 \text{ years}}{5 \times 10^9 \text{ years}} \right) \times 100 \]This will yield the percentage of Earth's history represented by abundant fossil evidence.

Solution for Abundant Fossil Evidence

Plug the numbers into the formula from Step 6:\[ \text{Percentage} = \left( \frac{540 \times 10^6}{5 \times 10^9} \right) \times 100 = 10.8\% \]Therefore, abundant fossil evidence represents about 10.8% of Earth's history.

Key concepts

Earth history

The story of Earth is ancient and complex, dating back approximately 5 billion years. This immense span of time is often broken down into smaller units to better understand the events and changes that have occurred over its vast years. Earth history encompasses everything from the formation of the planet itself, through geologic events like the creation of mountains and oceans, up to the conditions that allowed life to develop and thrive.

Understanding Earth's history helps us to comprehend the long processes that have shaped our planet. Scientists divide this immense period into different eons, eras, periods, epochs, and ages based on major geological or paleontological events. For instance, epochs such as the Pleistocene marks times when ice ages occurred. Earth's history serves as a grand narrative, laying out not only how our planet has transformed, but also how life has evolved along with it.

recorded history

Recorded history is the relatively small window of human experience that has been documented in written form. This began only around 5000 years ago, making it a tiny fraction in the sweeping timeline of Earth history. Yet, it is during this short span that humans have made significant advancements in technology, culture, and civilization.

Before recorded history, human stories were passed down orally and through artifacts. With the invention of writing, such as cuneiform by the Sumerians, a more reliable form of record-keeping began. This enabled historians to trace the development of societies and understand both monumental and everyday life in past ages. For context, when considering Earth's overall timeline, recorded history represents merely 0.0001%, highlighting just how recent human civilization is compared to the planet's entire existence.

hominids

Hominids, or humanlike ancestors, have been part of Earth’s story for roughly 5 million years. These ancestors include modern humans, as well as our extinct relatives like Neanderthals and Australopithecines. Such a timeline places the existence of hominids well within the later phases of Earth’s geologic timeline.

Current evidence shows that hominids evolved in Africa and gradually spread to different parts of the world, adapting to diverse environments. They developed tools, learned to use fire, and began the first forms of social organization. Despite this significant impact, their appearance marks only about 0.1% of Earth's history, illustrating not only the brief period that hominids have existed, but also the extensive span of time occupied by our planet before our ancestors emerged.

fossil evidence

Fossil evidence is crucial for understanding the development of life on Earth, with significant discoveries only appearing about 540 million years ago during the Cambrian period. This fossil record is mainly composed of hard parts of organisms like shells and bones, which can tell us a lot about past life forms.

Fossils act as time capsules, offering insights into past climates, ecosystems, and evolutionary histories. The first abundant fossil evidence from the Cambrian period marks an important turning point in the complexity and diversity of life, known as the "Cambrian Explosion." It represents about 10.8% of Earth’s history. Before this period, most organisms were simple and microscopic. Fossil evidence serves as a crucial tool for paleontologists to reconstruct past life on Earth and understand the evolutionary tree of life.

Cambrian period

The Cambrian period, starting about 540 million years ago, is one of the most significant chapters in the Earth's history. It marks a dramatic rise in the diversity and complexity of life forms, often referred to as the Cambrian Explosion. This event saw the advent of most of the major groups of animals, including the ancestors of modern-day species.

During the Cambrian period, organisms with hard shells and exoskeletons became common, leaving behind a rich fossil record. This period represents a mere 10.8% of Earth's total age, but it is a pivotal time when life on Earth truly began to flourish in complexity. It provides scientists with a clear window into how life evolved and gives context to the biological diversity we witness today. The Cambrian period's contribution to Earth's history underscores the rapid evolution and diversification of life that can occur in such a relatively short geologic time span.