Time Challenge: How to Illustrate a Billion Years?

What is a billion years?

A dizzying time scale

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

Why is it difficult to visualize a billion years?

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

Absence of cultural or historical landmarks

• The average human lifespan is about 80 years, which is infinitesimal compared to a billion years.
• Written human history goes back only 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 at 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 brain is not naturally equipped to process such large numbers. It evolved to process information at scales relevant to our survival and daily interaction with the world.
• Our senses are adapted to perceive changes on 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 brain uses heuristics (mental shortcuts) to process information efficiently. Large numbers and abstract concepts require additional cognitive effort and tools such as mathematics or visualizations to be understood.

Perception of linear time

• Our brain perceives time linearly and sequentially, which makes 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.

Analogies to visualize immensity

• Comparison with familiar distances: Imagine you move 1 millimeter per year. In a billion years you will have traveled 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 rose 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 a height due to erosion and gravity.
• Comparison with continental drift: In a billion years, a continent could theoretically circle the Earth. Tectonic plates move at an average speed 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 (circumference of the Earth). In reality, continents do not move in a straight line (subduction, collision, etc.), however, this calculation illustrates the immensity of this duration.
• Comparison with Darwinian evolution: In a billion years, biological evolution accumulates thousands of adaptations transmitted by natural selection. For perspective, hominids appeared about 7 million years ago, mammals 200 million years ago, vertebrates 500 million years ago. In 1 billion years, successive genetic mutations, filtered by natural selection, allow the transition from a simple unicellular eukaryote to a complex animal endowed 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 living things.

The limits of analogies

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