I’ve always been fascinated by how we humans perceive and understand the world around us. One area where our intuition often fails us is in comprehending vast stretches of geological time. We’re quite good at estimating the age of people or recent historical artifacts, but when it comes to landscape features, our brains tend to short-circuit.
This disconnect became starkly apparent to me while teaching a seminar course on the geological history of the Hawaiian Islands. To introduce students to the challenges of interpreting geological time, I gave them an unexpected first assignment involving images from the surface of Mars. The results were eye-opening and led me to reflect on how we perceive age in unfamiliar contexts.
I’ve created a video exploring this topic in more depth, using images from Mars to illustrate key points. I encourage you to check it out here:
Here I will summarize the main insights I made from this exploration of Martian geology and our perception of time.
The Mars Rover Assignment
To kick off my seminar, I asked students to visit NASA’s Mars Rover website and select an image captured by the Opportunity rover. Their task was to write a one-page description hypothesizing the history of the scene, including a timeline of events. In our next class, we discussed their interpretations and timelines.
Most students gravitated towards images featuring craters, recognizing them as key geological features. They generally understood the basic sequence of events: bedrock formation, impact event, and subsequent erosion. However, their estimated timelines revealed a striking misconception.
The Erosion Time Disconnect
The most glaring issue in students’ interpretations was their severe underestimation of erosion rates on Mars. Many suggested that the weathering and smoothing of crater features might have occurred over just 10-100 years. Some stretched their estimates to a few thousand years, but none came close to the hundreds of thousands or millions of years that Mars geologists estimate for these processes.
This miscalculation isn’t entirely surprising. On Earth, we’re accustomed to seeing significant erosion occur over human timescales due to water, plants, and other active forces. But on Mars, with its thin atmosphere and lack of liquid water, erosion happens at a glacial pace by comparison.
A Tour of Martian Features
To illustrate the vast differences in age between Martian features, let’s examine a few key examples:
- Fresh Craters Some craters on Mars appear remarkably “fresh,” with sharp, jagged rocks around their rims. While students often assumed these might be just a few years old, even these youthful-looking craters are likely at least 100,000 years old.
- Moderately Eroded Craters Craters with smoother rocks and partially filled interiors represent the next stage of erosion. These features, which students might have guessed to be a few hundred years old, are more likely in the range of hundreds of thousands to millions of years old.
- Ancient, Heavily Eroded Craters The largest, most eroded craters on Mars tell a tale of immense age. Endeavor Crater, for example, spans 16 miles in diameter but has been worn down to a shallow valley surrounded by eroded hills. Geologists estimate it could be 500 million years old – a timescale nearly impossible for us to intuitively grasp.
The Power of Wind… Given Enough Time
As students debated the processes responsible for Martian erosion, they correctly identified wind as the primary force. However, they struggled to accept just how long wind erosion would take to produce the observed features.
The reality is that Martian wind, while persistent, carries very little material and exerts minimal force compared to erosive processes on Earth. Estimates suggest that some Martian rocks might erode at a rate of only half an inch per thousand years. This snail’s pace of change is difficult for us to comprehend, accustomed as we are to the rapid environmental changes visible in human lifetimes.
Implications and Reflections
This exercise revealed how deeply ingrained our Earth-based intuitions about geological processes are. Even students who accepted the idea of an ancient universe struggled to apply that concept to specific landscape features. It’s a powerful reminder of how counterintuitive some scientific concepts can be, even for educated individuals.
This perceptual gap can be exploited by those promoting young-Earth ideologies. When someone claims that Martian features could have formed in just a few thousand years, it might not immediately strike the average person as absurd. It’s only through careful examination of evidence and rates of change that we can arrive at more accurate timescales.
My experience with these students underscores the importance of helping people develop a more robust understanding of geological time. It’s not enough to simply state that the Earth or Mars is billions of years old – we need to provide tangible examples and clear explanations of how we know this to be true.
Naturalis Historia 