Further experiments

“Hey, Rocky!” I call out from the lab. “Watch me pull a Taumoeba out of a hat!”

Rocky climbs up his tunnel from the control room. “I assume that is Earth idiom.”

“Yeah. Earth has entertainment called ‘television’ and—”

“Do not explain, please. You have findings, question?”

Just as well. It would take a long time to explain cartoons to an alien. “I have some results.”

“Good good.” He hunkers down into a comfortable sitting position. “Tell findings!” He tries to hide it, but his voice is just a touch higher in pitch than normal.

I gesture to the lab apparatus. “This functions perfectly, by the way.”

“Thank. Tell about findings.”

“My first experiment was Adrian’s environment. I added Taumoeba and a slide covered in Astrophage. The Taumoeba survived and ate it all. No surprise there.”

“No surprise. Is their native environment. But proves equipment works.”

“Exactly. I did more tests to learn Taumoeba’s limits. In Adrian air, they can live from minus 180 degrees Celsius to 107 degrees Celsius. Outside that range they die.”

“Impressive range.”

“Yes. Also, they can survive in a near vacuum.”

“Like your fuel tanks.”

“Yeah, but not a total vacuum.” I frown. “They need carbon dioxide. At least a little bit of it. I made an Adrian environment but put argon in instead of carbon dioxide. The Taumoeba didn’t eat anything. They stayed dormant. Eventually they starved to death.”

“Expected,” he says. “Astrophage need carbon dioxide. Taumoeba from same ecology. Taumoeba also need carbon dioxide. How they get carbon dioxide in fuel tanks, question?”

“I had the same question!” I say. “So I did a spectrograph of my fuel-bay sludge. There’s a bunch of CO2 gas dissolved into the liquid.”

“Astrophage probably have carbon dioxide inside. Or decomposition creates carbon dioxide. Some percentage died in fuel tanks over time. Not all cells are perfect. Defects. Mutations. Some die. Those dead Astrophage put carbon dioxide in tanks.”

“Agreed.”

“Good findings,” he says. He starts climbing back down.

“Wait. I have more. Much more.”

He stops. “More, question? Good.”

I lean against my lab table and pat the tank. “I made Venus in the tank. But not quite Venus. Venus’s air is 96.5 percent carbon dioxide and 3.5 percent nitrogen. I started with just the carbon dioxide. The Taumoeba were fine. Then I added the nitrogen. And the Taumoeba all died.”

He raises his carapace. “All die, question? Sudden, question?”

“Yes,” I say. “In seconds. All dead.”

“Nitrogen…unexpected.”

“Yeah, very unexpected!” I say. “I repeated experiment with Threeworld’s air. Carbon dioxide only: The Taumoeba were fine. I added in the sulfur dioxide: The Taumoeba were fine. I added the nitrogen: Boom! All the Taumoeba died.”

He taps a claw absently on the tunnel wall. “Very very unexpected. Nitrogen harmless to Erid life. Nitrogen required by many Erid life.”

“Same with Earth,” I say. “Earth’s air is seventy-eight percent nitrogen.”

“Confusing,” he says.

He’s not alone. I’m just as baffled as he is. We’re both thinking the same thing: If all life evolved from a single source, how can nitrogen be critical to two biospheres and toxic to a third?

***

Chapter 24