Dear Marshall,

Sometimes I get x-rays at the veterinarian. They work by sending a small amount of powerful energy—called radiation—through my body. X-rays only contain a small amount of radiation. Too much radiation would harm my cells.

The organisms most likely to survive extreme radiation might be microbes. These creatures are so tiny you need a microscope to see them.

To learn more, I talked with my friend Cynthia Haseltine. She’s a microbiologist at Washington State University. She studies extremophiles. These microbes love intense environments. Boiling heat? Freezing cold? Blistering acid? Yes, please.

Haseltine told me the amount of radiation an organism can survive is measured in grays. Just 5 grays of radiation will kill a human. Here are five organisms that can survive way more than that.

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Escherichia coli: 500 grays

The first creature is one of your closest neighbors. It’s a type of bacteria that’s inside your body. Some kinds of E. coli make people sick. That’s why we wash our hands and make food carefully. But E. coli also lives in your intestines and helps you break down food. It can survive 10 times the radiation a human can. Plus, it adapts quickly. If blasted with radiation, it would probably become resistant—or able to withstand even more radiation.



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Sulfolobus microbes: 500 grays

These microbes live in boiling-hot mud pots—like those found in Yellowstone National Park. They thrive in the hot, stinky-sulfur mud. Just like E. coli, they would probably become more resistant when exposed to radiation.




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Tardigrades: 4,000 grays

Tardigrades are the only animals tough enough to make the list. But these animals are tiny. You need a microscope to see them. They’re sometimes called water bears because they look like gummy bears with eight stubby legs. Tardigrades can survive extreme cold, heat and pressure. They can even survive in outer space. They can withstand 800 times more radiation than a human can.



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Deinococcus radiodurans: 5,000 grays

Scientists discovered this microbe when they were testing new ways to preserve food. They beamed radiation at a can of meat, but it spoiled anyway. They found D. radiodurans inside the can. This creature can handle freezing-cold and acid. It can live in a vacuum. That’s space with nothing in it—not even air. It even survived three years in outer space.



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Thermococcus gammatolerans: 30,000 grays

My jaw dropped when I heard how much radiation this microbe could handle. That’s 6,000 times the radiation a human can survive! This microbe lives deep in the ocean near underwater volcanoes. It loves heat and pressure.




Thinking about the incredible life on Earth makes me wonder about other mysteries in the universe.

“These are the organisms that are probably out there in our local solar system if we’re looking at life off Earth—because everything’s extreme out there,” Haseltine said. “So, they may be out there surviving apocalyptic conditions right now.”

Now that’s radiant.


Dr. Universe