It’s almost impossible to wrap your mind around the sheer magnitude of geologic time. Earth was formed 4.6 billion years ago – what does that number even mean, compared to quantities of time that are more familiar to us? How far apart were various events in earth’s development? For earth science today, we converted the timescale of earth’s history to distances along a 100-foot timeline.
As luck would have it, the distance from our right-hand neighbors’ driveway to our left-hand neighbors’ driveway is almost exactly 100 feet. We measured out the distance and marked the ends “birth of the earth” and “now.” Then I asked Alex to walk along the pathway and tell me where she thought various things happened:
Formation of the moon
Age of oldest rocks on earth
First microscopic life
Homo sapiens sapiens
Recorded human history
We drew symbols along the curb in pink to mark her guesses. Then we began to measure out the real timescale. I had Alex draw out one foot of the tape measure, and told her that it represented 46 million years. Then she drew out one inch: four million years. We began to mark off events with chalk and taped-down post-it note labels.
Three feet from the start line, the moon was formed.
Fourteen and a half feet after that, water condensed into oceans. The oldest rocks on earth have also been dated to that point.
Four and a half feet after that, microscopic life.
Alex guessed that mammals appeared about 20 feet from the present day on our timeline. Instead, that’s where we put the first appearance of multicellular life. (You can see all of our timeline events and their dates here). The dinosaurs appeared just a few feet from the present.
Hominids appeared one inch from the end of our 100-foot timeline.
Homo sapiens sapiens, modern humans, appeared 1/8 of an inch from the end.
And recorded history? All the wonders of history we’ve studied ranging back to Ancient Egypt? We pulled out an inch from the tape measure. At the scale of our timeline, the entire length of recorded human history represents one one-thousandth of an inch.
We walked the length of the timeline several times, trying to comprehend the scope of it. Here’s a picture I took standing at the present. The kids are at standing at the origins of the earth. The two labels you see in the foreground, by the orange cup, show the first appearance of vertebrates and land plants: that long after earth began.
We considered the Himalaya mountains, the highest on earth. They began forming 30 million years ago, just 8 inches from the present on our timeline. We considered that eight-inch stretch compared with the vast total length of our line. How many mountain ranges could have built up and worn away, built up and worn away, in the whole of that time?
Geologic time: unfathomably long. That’s the first real lesson as you begin to study earth science.