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Panel 1

Image is of character with a blue background. The character states, “Have you ever wondered about that green layer of “slime” we see sometimes on lakes?”

Panel 2

Image is of character with a blue background. The character states, “Well, it’s not always algae. It can be a layer or cyanobacteria!”

Panel 3

Image is of character diving into a lake, where a group of green microbes is circled and labeled as Cyanobacteria, and a group of red microbes deeper in the lake is circles and labeled as Photoferrotrophs. The character states , “Cyanobacteria are microbes that need light and oxygen to live. They live near the surface of lakes. But what lives deeper? In some lakes, there isn’t any oxygen at the bottom. Microbes that live here have a different lifestyle, replacing oxygen with another molecule, like iron.” The attached text box reads, “We can study ancient metabolic processes without time travel, but studying microbes in lakes that are analogs for a point in Earth’s history when there was no oxygen.”

Panel 4

Image is a clock with the arrows pointing at the time “2.5 billion years ago.”

The attached text box reads, “Some of these metabolic processes are ancient, allowing insight into the lives of microbes that lived over 2.5 billion years ago, before the Earth was oxygen rich. These microbes are contributing to elemental cycles, which are like the water cycle but featuring compounds such as iron or carbon rather than water.”

Panel 5

Image consists of three frames: energy sources, electron sources and carbon sources. Frame 1 has an image of the sun, labeled as light, and a rock. Frame 2 contains oxygen, nitrate, iron and sulfate. Frame 3 contains citrate, glucose and acetate, the three of which are labeled as organic carbon; and carbon dioxide, labeled as atmospheric carbon. The attached text box reads, “All microbes need one of each: (1) Energy source, (2) Electron Source, (3) Carbon source.

Panel 6

Image of reddish-brown microbes, labeled “Photoferrotrophs.” The word “photoferrotrophs” is broken down, with an arrow leading from the portion “photo” to an image designating the sun as the energy source for this organism, and an arrow leading from the portion “ferro” designation iron as the electron acceptor for this organism* Text associated with this image reads, “One interesting group of microbes are the photoferrotrophs. (Carbon source is carbon dioxide.)

Panel 7

Image consists of iron(3+) being spewed out of a hydrothermal vent, photoferrotrophs consuming the iron (3+) and producing iron (2+), which falls to the ocean floor and forms layers of iron. A clock in the image points at the time “long ago.” Text box 1 reads, “Photoferrotrophs are important to study since they’re thought to have played a role in creating banded iron formations (BIFS)– layers of iron oxide deposited on the ocean floor billions of years ago.” Text box 2 reads “Hydrothermal vents are underwater volcanos. They were common on ancient Earth and still exist today!”

Panel 8

Image is of a hill that has been cut to allow a road to run through it rather than over it, exposing the rock layers beneath the surface. The red iron layer that was laid down long ago (in panel 7) is noted, and there is a clock pointing at the time “present.” Above this panel is text asking “Where are the layers now?” To the right of it is the character, stating “These red layers are the iron layers that were deposited on the ancient ocean floor. We can see them in the rock today, like in this hill cut through by a road.”

Panel 9

Image is of Mars from space. Text box above the image reads “If there are microbes on Mars, they could be photoferrotrophs because photoferrotrophs only need light and iron to live. Mars has both!” The text box below the image reads “This research is going to seaerch for photoferrotrophs at the bottom of lake Brownie, MN. We can search for “biosignatures,” which are evidence of these bacteria in the rock record, like fossils! This technique could be used to search for evidence of life on other worlds such as Mars!”