When it comes to developing an illustrated information graphic, sometimes you don’t really know what sorts of details you’re going to need until you dive in and start drawing. That was certainly the case for a timeline of the events that led to the development of Earth’s oceans, which appeared in “Oceans from the Skies” by David Jewitt and Edward Young in the March issue of Scientific American.

When editor Lee Billings suggested a storyboard-like timeline sequence, I thought immediately of graphics artist John Grimwade. Often we use articles about planetary science as an excuse for producing lush space paintings, and I love cosmological scenes as much as the next person, but this topic was a bit tricky.

We needed to show variables that wouldn’t lend themselves to figurative representations at this macroscopic scale, like water molecules hidden inside the planet. Grimwade is brilliant at graphically walking readers through scenarios, and I knew he could develop a visual language that would allow us to represent macro and microscopic information in one view. So I sent him a proposal for an eight-step timeline based on Billing’s article summary, and a full spread (two facing pages) to work with.

Here’s a peek at one of Grimwade’s preliminary concept sketches–very much a work-in-progress. Grimwade had introduced a color scale to represent water content–including both liquid on the surface and the relative concentration of water molecules locked in rocks and minerals below the surface–from relatively dry (red) to relatively wet (blue). He also created what I like to refer to as a “bombardment o’meter” (dot scale) to help convey the level of asteroid and comet activity. But we needed more guidance from the scientists who authored the piece to figure out the subsurface coloration, as we didn’t have all the details for mantle and core moisture content. (Note that the colors used in the sketch below do not represent the science accurately. This was simply an experiment, to show how color might be used in general).

Preliminary concept sketch by John Grimwade

Jewitt and Young gamely considered our request for subsurface moisture content information for each step. But they started to hedge, as it became clear that temperature was also an important variable to portray, and as they aptly pointed out, red intuitively reads as “hot” rather than “dry.” Young then developed a detailed set of cartoons, to help us understand all of the details.

Schematics by Edward Young

Grimwade incorporated these new details into the graphic, adding in volcanic activity and degassing events, and tried out a dual color scale at my request. A gradient from black to blue would now represent water content, and black to red would represent temperature.

Updated sketch by John Grimwade

Color-coding became more intuitive and less structured as the piece developed, and the graphic skewed a bit more literal and detailed and less symbolic than originally anticipated with the addition of volcano, cloud, and continent icons. Here’s the final graphic, as it appears in the March issue.

Final graphic, as it appears in the March 2015 issue of Scientific American. Illustration by John Grimwade, globe by Visible Earth, NASA

Part of me misses the idea of simply portraying moisture content, temperature, and level of bombardment in a minimalist manner. There was something neat about the idea of stripping things down to the bare bones, and making change over time of those three major variables the sole focus of the graphic. But as I learned more about the processes at play, it became clear that we’d be stripping out too many other important details, like volcanic activity and cloud formation–details that resulted in a more complicated, but more accurate and nuanced, representation of the history of water on Earth.