The Earth is roughly four and a half billion years old. During most of that time—i.e. over the course of some four billion years—the geological and biological development on our planet happened unbelievably slow. How can we possibly form even a faint idea of this unimaginable process that is the history of the Earth? Of how it evolved from a body of molten rock into a planet with continents, an atmosphere, a population of seven and a half billion people and a climate problem? I have always been fascinated by this intellectual challenge. Not only is it overwhelmingly complex, but also the incredible duration of time is enormously difficult to picture.
It is when information graphics manage to provide a glimpse of the unconceivable, to shed some light on the unimaginable that they prove their inherent potential as a tool for fostering insight. This poster was published in 1975 by the United States Geological Survey, and it certainly does deserve some of that credit. It creates a compelling, if condensed visual history of our planet. The US Geological Survey, a scientific authority for the research on geology, climate and environmental issues, routinely hands out maps, writings and other documentation to inform the public, and this poster is part of their general interest publication series.
What a visionary abstraction: the poster represents geological time as a narrow plateau spiraling back into the depths of history. On top of this plateau, geological and biological processes are unfolding, and the historical epochs are labelled along the sides. On the front end of the spiral in the lower center of the graphic, we can see our present epoch, and the fact that this tiny sliver represents as many as the past 11,500 years (more than 140 times our average life span) already gives a glimpse of the enormous chunks of time we’re looking at.
To put to this ingeniuos graphic invention into context, take a look at this standard Geological Time Scales (image below), based on stratigraphic research. It is basically a long column with layers stacked upon each other. While most layers look pretty equal through all eras, the time stamps along each column correct this picture. The short column on the right, shaded in pink tones, represents the four billion years of the Precambrium (i.e. eighty-eight percent of Earth’s history). In contrast, the column on the left in greenish/yellowish shades represents only the past 145 million years (i.e. three percent of Earth’s history).
From the beginning of the Cambrium around 541 million years ago, an enormous amount of animal species evolved and a variety of life-forms „exploded“ on this planet. This is when many histories of our planet would start taking a closer look onto what had happened during each period, while cutting short the enormous duration of time that had passed before. Our Time Spiral here has the precambrian era pull out backwards into the dust elegantly, so it can maintain an impression of its unconceivable duration without having to spell it out in much detail.
The periods since the Cambrian epoch, on the other hand, are displayed very eloquently, almost like in a children’s panorama. See the little arthropods climbing up the spiral in the Cambrian period. Look at the variety of dinosaurs and rich wildlife that populate the terrain all through the Mesozoic Era. Along the edges, mountains evolve, volcanos spit out ashes and dust, plants pop out to form lush habitats.
Of course, this imaginative piece was always intended to be a popular explanation. Other than the stratigraphic chart above—which was designed as a means of communicating scientific data, and which to this purpose is regularly updated as new research is published—this poster is meant to help the imagination of readers who are not paleontologists or experts of historical geology, and who are not familiar with the succession of eras in the history of Earth. However, this piece has managed to create such a convincing image of our planet’s past, that still today—fourty years after it has been designed—it is circulating widely and is used on many a website, including some major Wikipedia sites on the topic. Not bad for a popular poster, is it?