Time Challenge: How to Illustrate a Billion Years?

What is one billion years?

In one billion years, at a rate of 5 millimeters per year, the Himalayas would rise by 5,000 kilometers. In one billion years, at a rate of 1 millimeter per year, you would have traveled 1,000 kilometers. In one billion years, at a rate of 4 centimeters per year, a continent could circle the Earth. In one billion years, Darwinian evolution allows the transition from a simple unicellular eukaryote to human intelligence.

Why is it difficult to visualize a billion years?

The concept of a billion years far exceeds the time scale humans are accustomed to. Our minds are designed to grasp relatively short durations, such as a day, a year, or even a century. A billion years encompasses periods so vast that they exceed anything we can relate to our experience or collective memory.

Unlike shorter durations, there are no personal events or experiences to represent a billion years. Changes at this scale, such as the formation of mountains or the evolution of stars, are imperceptible on a human scale. Without concrete reference points, it is difficult to conceptualize such time scales.

Absence of cultural or historical reference points

• The average human lifespan is about 80 years, which is infinitesimal compared to a billion years.
• Written human history only goes back about 5,000 years, which is extremely short compared to a billion years.
• Major geological events, such as the extinction of the dinosaurs 66 million years ago, seem recent on this scale.
• The ability to handle large numbers is relatively recent in human history. It is the result of cultural and technological developments, such as mathematics and science, which are not innate but acquired through education and practice.

Cognitive difficulties

• Our brains are not naturally equipped to process such large numbers. They have evolved to process information at scales relevant to our survival and daily interaction with the world.
• Our senses are adapted to perceive changes over relatively short time scales. For example, we can easily perceive the passage of seconds, minutes, or hours, but not thousands or millions of years.
• Our brains use heuristics (mental shortcuts) to process information efficiently. Large numbers and abstract concepts require additional cognitive effort and tools like mathematics or visualizations to be understood.

Perception of linear time

• Our brains perceive time linearly and sequentially, making it difficult to understand exponential scales. For example, we can imagine 10 years, 100 years, or even 1,000 years, but beyond that, the numbers become abstract. A billion years represents such an immense accumulation of time that it defies our ability to conceptualize it intuitively.

How to illustrate a billion years?

To grasp such a time scale, it is easier to use analogies and spatial visual representations.

• Comparison with familiar distances: Imagine moving 1 millimeter per year. In a billion years, you would travel 1,000 kilometers. 1,000 years = 1 meter (one step). 1 million years = 1 kilometer (a walk). 1 billion years = 1,000 kilometers (a car trip).
• Comparison with mountain formation: In a billion years, the Himalayas (8,849 meters) would rise 5,000,000 meters. The Himalayas have risen at an average rate of about 5 millimeters per year. In 1,000 years, the Himalayas would rise 5 meters. In 1 million years, 5 kilometers. In 1 billion years, 5,000 kilometers. In reality, mountains cannot reach such heights due to erosion and gravity.
• Comparison with continental drift: In a billion years, a continent could theoretically travel around the Earth. Tectonic plates move at an average rate of 4 cm per year. In 1 million years, a continent moves 4,000,000 cm (40 km). In 1 billion years, it moves 40,000 km (Earth's circumference). In reality, continents do not move in a straight line (subduction, collision, etc.), but this calculation illustrates the immensity of this duration.
• Comparison with Darwinian Evolution: Over a billion years, biological evolution accumulates thousands of adaptations transmitted through natural selection. For perspective, hominids appeared about 7 million years ago, mammals 200 million years ago, and vertebrates 500 million years ago. Over 1 billion years, successive genetic mutations, filtered by natural selection, allow progression from a simple single-celled eukaryote to a complex animal with nerves, muscles, a complete digestive system, and adaptive behaviors. This is the full power of the Darwinian mechanism: slow, incremental, but capable, over such durations, of radically transforming the nature of life.

Although distances and durations are distinct concepts, comparing them can be logical and useful for understanding cosmic scales. These analogies illustrate how immense a billion years is, even on the scale of the slowest processes.