Issues in Earth Science

“Eww, There’s Some Geology in my Fiction!”

Issue 19, May 2025

Teacher Resources

Suggestions for Activities and Discussions to accompany Readings of

Feedstock by Scott Schad

It’s been a while since we did an experimental Teacher Resources, so we’re going to take a look at some experiments you can do in the classroom that simulate, in some ways, tests of Martian regolith that look for evidence of life. However, first we are going to consider a classroom discussion that might arise from this story that is very relevant to modern issues on Earth.

Part 1: Discussion

The story, Feedstock, centers around the discovery of life on Mars that might be threatened by the mining operations ongoing there and the response of the mining company to that possibility. There are real-world current things happening on Earth that are very much like this scenario.

To set the stage, science, exploration, and technological developments always have consequences, both negative and positive. For example, the scientists who studied nuclear processes through the first half of the 20^th century are often criticized because of the use of that knowledge in making nuclear bombs dropped on Japan during World War II. However, if no new understanding had ever been pursued because it carried potential negative consequences, then humanity would never have started the first fire, sharpened the first flint knife, or sealed the keel of the first water vessel. All of these things have been used for negative purposes.

The terrible truth is that all discovery has been used for both good and bad. Should we therefore do nothing and discover nothing so as to avoid the bad? Or do we do it all so as the pursue the good? Different people may come down on different sides of this question, however, history has shown that those who pursue the discoveries will, in the end, likely win the day, whether good or not. Those who had fire, knives, and ships conquered those who did not (ouch, people should be nicer to each other, don’t you think?).

The (somewhat similar) moral question for us today, that bears not only on the story Feedstock but on many modern challenges, is how much weight do we give our own human needs and wants, and how much weight do we give the existence of other creatures that may be affected by our actions?

Mining the floor of the deep ocean for manganese nodules and other resources is an issue not unlike the problem in Feedstock. Our hunger for more and more technological devices and infrastructure drives a need for copper and other natural resources and that need turns our eyes to the oceans. Oceans comprise more than 70% of the Earth’s surface and the deposits of the sea floor are a treasure trove of mineral resources. They are also a treasure trove of highly fragile and rare ecosystems. The extreme long-term stability of these deep ocean environments means that the ecosystems there are not adapted for disruption, and the disruption of mining might destroy them. Is the value of the resources we might extract worth that loss?

Do some searching online to learn about mining the sea floor and its ecological consequences, and then have discussions/debates in groups or as a full class to explore this complicated issue.

Part 2: Experimental investigation of biological activity

Our exploration of Mars has always included an interest in finding life there. When astronomers turned their telescopes on Mars in the late 1800s and sketched what looked like channels, some speculated that these were canals, constructions of an advanced society. Viking I, the first ship from Earth to successfully land on Mars in 1976, carried equipment to test the soil for presence of microscopic life. The last two decades of exploration on Mars has carried the explicit goal of looking for water as a prerequisite for life (as we know it). (Editor’s note: as a geologist, the pursuit of the headline “Life discovered on Mars” has always annoyed me—why can’t people be excited by the headline “Rocks discovered on Mars!”)

The Viking lander did a number of tests looking for metabolic activity, including looking for generation of gases that result from respiration, such as carbon dioxide (CO₂).

Students can do a much simpler experiment in the classroom to try to detect biological activity in soil or sediment samples.

Consider the following skeletal experimental design:

Collect 2 cup-sized soil samples from a moist, organic rich source, like a garden or farm field that has been well maintained with compost over the years. Collect a third cup of sediment that is likely to be sterile, such as sand from a local hardware or landscaping company. Heat one of the soil samples in the oven to a temperature, say 350F, where living things are unlikely to survive.

Get four pint-sized canning jars with lids. Put each of the three samples in each of three jars Keep the fourth jar empty of soil samples to use as our control experiment. Put a drop of bromothymol blue solution in each jar (perhaps in a small container or on a piece of glass that is laid onto the soil sample just prior to closing the jar). Note that it is critical to the experiment that each drop of bromothymol blue be of exactly the same concentration, mixed with distilled water and kept in a clean vessel and covered until use to minimize air exposure and so that no drop has been exposed to air longer than another. Seal up each jar with the lid and begin monitoring the color of the Bromothymol Blue. Record the time it takes for the drop of bromothymol blue to change color (from blue to green to yellow) in each of the jars.

Interpretation: Bromothymol blue reacts with CO₂ in air and changes color due to changes in pH. More CO₂ will result in a faster change in color. Do you see any patterns in your results that suggest that you can detect the presence of life (or at least metabolic activity) in the samples? Explain!

Your experiments might have some complexities to interpret. What did you expect to happen and why? Did you see any results that you didn’t expect or that seem inconsistent with the model (explanation) that you are developing? It’s ok in science, and in fact desirable, to recognize when your experiments did not yield the result that you expected or the result that seems ‘right’. What might explain your results if you did not get what you expect? Do you need to adjust the concentration of your bromothymol blue? Do you need to change how it is introduced and contained in your experiment vessel? Is your soil sample perhaps not as ‘living’ as you might expect for a typical soil (there are more living organisms in a ‘living’ soil sample than there are people on Earth!) You should also recognize that measuring the production of CO₂ with the bromothymol blue might not be sufficiently sensitive to see any effect even if it ‘seems like’ you got the right answer. If so, can your students figure this out from their results?

The results from the Viking landers also had some complexities, despite the fact that there were three distinctly different tests and each involved measurements more sophisticated than using bromothymol blue. Some people thought one of the tests (which introduced radioactive carbon into the samples as nutrients and then checked whether the radioactive carbon found its way into carbon dioxide in the atmosphere, suggesting metabolic conversion) showed that life had been detected. However, the other tests showed no meaningful presence of carbon in the soil to begin with which seemed inconsistent with that result. In the end, most scientists thought, at best, the test for life was ambiguous and maybe even indicated an absence of life.

Real experimental science is about figuring what your actual results mean, not trying to prove some preconceived ‘right’ answer! What do your results tell you about your experiments? Sometimes, ambiguity is the right answer! Other times, you can say things with confidence. Being able to tell the difference is a primary objective of authentic science as a practice.

Part 3: Identifying the evidence for Martian life in the story Feedstock.

Below is a section of the story where the protagonist explains the evidence for life on Mars. Read the text and try to identify exactly that that evidence is (make a list of observations). Try to explain the evidence in your own words (for each item in your list, write why it is evidence). Can you put all the pieces together and convince one of your classmates?

“Very well. It has been known for some time that many regions on Mars contain subsurface ice. Mining this ice to turn it into water is an energy-intensive process. Indeed, our present mining industries were energy-constrained until I discovered deep reserves of liquid water. If these water reserves are intelligently developed, Margin can look forward to many decades of lucrative work.

"Aerotek renewed my contract in order for me to assay possible liquid water deposits in your stage three mining concession, or as you call it, your Paradox project. I chose to begin by comparing known reservoirs to establish a prudent baseline case.”

Hobbs, proving to be the more vocal of the corporate bookends, interrupted, “And so, after renewing your assignment, you began by wasting Margin's money, telling us what we already knew!”

“Not at all,” Frank remained unruffled. “A base case provides essential calibration for any forecast. It also clearly establishes knowns, which in your case, were not so.”

Culbertson coughed. “Margin was quite on top of water quality issues, Frank.”

“Yes sir, but only in a qualitative sense. Margin owns exactly one fluorescence spectrometer, which hardly provides a robust method of analysis. By expanding the scope of my examination I provided the means for you to measure the scale of what now looks like a planet-wide problem.” Frank paused while Dobbs looked at the ceiling and exhaled loudly, then he continued.

“I collected certain facts and mapped them. Without exception I found that in each region where Margin has discovered liquid water a distinct salinity profile exists. Whereas your shallow exploratory wells tapped fresh waters, your later and deeper wells found progressively higher salinities. Your own corrosion maintenance reports bear this out.”

Culbertson shifted his overfed frame, creaking his chair. “Frank, we all know the history of water on Mars. There is no need to give us a miner's introductory course.”

“Yes, we all know that the water essential for any expansion of our operations on Mars originally came from glaciation. Our best estimates put last-stage glaciation from 50,000 to 100,000 years ago. But gentlemen, glaciers consist of frozen fresh water. Where did the salt come from?”

“Oh come now,” Culbertson frowned, “surely no one disputes that salt came from the bedrock itself as water flowed through it? Do you challenge that?”

“In your stage one mining area my work clearly shows that, in fact, salts dissolved out of the host rock. But in all other cases, and in the rest of Margin's concessions, no suitable rock formation exists to provide the salts. Further, it is only in the remaining cases that we find clathrates.”

“What?” Dobbs shook off his bored stupor at the unfamiliar word.

“Gas hydrates. Think of clathrates as ice cages. Microscopically, they resemble linked geodesic spheres, each just big enough to contain one molecule of methane gas. We find them at the extreme updip ends of the water reservoirs, closest to the cold surface of the planet.”

Culbertson addressed an aside to Dobbs: “We know all about these gas-ice hydrate deposits. They've never proven to be a problem for our operations.”

“And yet,” Frank said, “no one before me attempted to analyze the gas that they contain. Isotopically, the methane gas trapped in these small ice cages is identical to Archaebacteria-sourced gas on earth.”

“Who cares?” Hobbs was back on point.

“We should all care, Mr. Hobbs, because all lines of evidence converge. Take the organic carbon values of the seal rocks encasing your aquifers, for example. Some measurements exceed 20% carbon by weight. Or look at the obvious link between bacterial generation of methane and bicarbonate production. This ties to the increased alkalinity due to carbon dioxide being turned into bicarbonate at the bottom of your reservoirs.”

Below is the paragraph where the protagonist summarizes the evidence. How does the summary compare with the list you constructed for evidence for life? Can you focus your understanding of the evidence even more based on this? Does it offer new evidence that wasn’t cited before? Is there evidence cited before that isn’t repeated here?

“Yes sir. By alien life forms comparable to Archaebacteria, living in subsurface communities in fresh water halos above the alkaline waters. I've spent the last two years testing water samples across your concession areas and they clearly show the alien biota as assemblages of flimsy cells and filaments no different from their counterparts on earth. The microbes appear to be eating the organic matter in the high-carbon shales which seal your aquifers. They excrete both carbon dioxide gas, which drives the bicarbonate formation, and methane gas, which ascends to take up residence in the ice cages.”

Connecting the Next Generation Science Standards

The discussion, the experimental activity, and the identifying the evidence activity above support the following NGSS performance expectations:

MS-ESS2-1

HS-ESS2-6

MS-LS2-3, MS-LS2-4

HS-LS2-6

Students can exercise skills in the practices of:

1. Planning and Carrying Out an Investigation

2. Analyzing and interpreting data

3. Engaging in Arguing from Evidence

4. Obtaining, Evaluating and Communicating Information

Students experience the crosscutting concepts of:

1. Cause and effect: mechanism and explanation

2. Systems and system models

3. Energy and matter: flows, cycles and conservation

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The Teacher Resources for Feedstock are written by Russ and Mary Colson, authors of Learning to Read the Earth and Sky.

Return to Feedstock by Scott Schad

Return to “Eww, There’s Some Geology in My Fiction.”

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