If we do find alien life, what kind will it be?
Three lines of evidence point to the idea of complex, multicellular alien life being a wild goose chase. But are we clever enough to know?
Adam Frank is a professor of astrophysics at the University of Rochester and a leading expert on the final stages of evolution for stars like the sun. Frank's computational research group at the University of Rochester has developed advanced supercomputer tools for studying how stars form and how they die. A self-described “evangelist of science," he is the author of four books and the co-founder of 13.8, where he explores the beauty and power of science in culture with physicist Marcelo Gleiser.
- Everyone wants to know if there is alien life in the universe, but Earth may give us clues that if it exists it may not be the civilization-building kind.
- Most of Earth's history shows life that is single-celled. That doesn't mean it was simple, though. Stunning molecular machines were being evolved by those tiny critters.
- What's in a planet's atmosphere may also determine what evolution can produce. Is there a habitable zone for complex life that's much smaller than what's allowed for microbes?
"Do you think we are alone?" That question is, without fail, one of the first things people ask me when they learn I'm an astronomer. And I get why. It's also the question I most want an answer for. But that answer may depend a lot on what kind of life the universe favors (if it favors any at all). So, the question I want to briefly touch on today is how common will it be for any life that appears on any planet in the universe to start climbing up the evolutionary ladder of complexity?On Earth, the history of life is mainly a story of single cells. Earth's origin lies some 4.5 billion years ago, and the best fossil records put the emergence of life as single-celled creatures about a billion years later. After life's first appearance, almost two billion years go by during which all evolutionary activity was on those single-celled organisms. There was some really amazing biochemical machinery evolving within those little cells but if you are interested in multicellular creatures, they don't appear until sometime around 700 million years ago.
... if there is one thing we know is true, it's that nature is more clever than we are. That means it may know lots of ways to produce animals without oxygen around or even in the presence of buckets of CO2.
What are we to make of this incredibly long run of Earth as Planet Bacteria? (Note, there were actually other kinds of single-celled creatures too). Well, it certainly tells us that evolutionary success does not demand multicellularity. During these long eons, life invented the most amazing array of nano-machines for a jaw-dropping variety of purposes. For example, single-celled critters invented photosynthesis for turning sunlight into sugars, metabolisms for turning sugars into energy, and complex intracellular transport mechanisms to move stuff where it was needed and get rid of waste. Earth before plants and animals was already a fertile place full of life that had, in its way, become spectacularly complex at least on the level of biochemistry.
Given the long run of this version of Earth, it may be that there is no reason that more complex life should be expected to form in all or even most cases on other planets.
Protozoa—a term for a group of single-celled eukaryotes—and green algae in wastewater, viewed under the microscope.
Credit: sinhyu via Adobe Stock
Another way the story of life on Earth might not get repeated elsewhere in the cosmos relates to the composition of planetary atmospheres. Our world did not begin with its oxygen-rich air. Instead, oxygen didn't show up until almost two billion years after the planet formed and one billion years after life appeared. Earth's original atmosphere was, most likely, a mix of nitrogen and CO2. Remarkably it was life that pumped the oxygen into the air as a byproduct of a novel form of photosynthesis invented by a novel kind of single-celled organism, the nucleus-bearing eukaryotes. The appearance of oxygen in Earth's air was not just a curiosity for evolution. Life soon figured out how to use the newly abundant element and, it turns out, oxygen-based biochemistry was supercharged compared to what came before. With more energy available, evolution could build ever larger and more complex critters.
Oxygen may also be unique in allowing the kinds of metabolisms in multicellular life (especially ours) needed for making fast and fast-thinking animals. Astrobiologist David Catling has argued that only oxygen has the right kind of chemistry that would allow for animals to form on any world.
Atmospheres may play another role in what can and can't happen in the evolution of life. In 1959, Su-Shu Huang proposed that each star would be surrounded by a "habitable zone" of orbits where a planet would have temperatures neither too hot nor too cold to keep life from forming (i.e. liquid water could exist on the planet's surface). Since then, the habitable zone has become a staple of astrobiological studies. Astronomers now know that the outer part of the habitable zone will be dominated by worlds with lots of greenhouse gases like CO2. A planet in a location like Mars, for example, would require a thick CO2 blanket to keep its surface above freezing. But all that CO2 could present its own problems for life. Almost all forms of animal life on Earth, including sea creatures, die when placed in CO2-rich environments. This has led astronomer Eddie Schwieterman and colleagues to propose a habitable zone for complex life: A band of orbits where planets can stay warm without requiring heavy CO2 atmospheres. According to Schwieterman, animal life of the kind we know would only be able to form in this much thinner band of orbits.
So, we have three lines of evidence that may suggest multicellular life (including thinking animals) may not be the road most taken across the universe. If this were true, then the galaxy might be awash with life but be sparse in terms of tentacles, paws, or boots on the ground.
Now, before your shoulders sag in sadness, it's important to note some facts. First, there are likely 400 billion planets in our galaxy alone. This provides a lot of leeway for experimentation. Second, if there is one thing we know is true, it's that nature is more clever than we are. That means it may know lots of ways to produce animals without oxygen around or even in the presence of buckets of CO2.
We just won't know until we start looking. And here is the good news. We finally are ready to start looking.
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Are "humanized" pigs the future of medical research?
The U.S. Food and Drug Administration requires all new medicines to be tested in animals before use in people. Pigs make better medical research subjects than mice, because they are closer to humans in size, physiology and genetic makeup.
In recent years, our team at Iowa State University has found a way to make pigs an even closer stand-in for humans. We have successfully transferred components of the human immune system into pigs that lack a functional immune system. This breakthrough has the potential to accelerate medical research in many areas, including virus and vaccine research, as well as cancer and stem cell therapeutics.
Existing biomedical models
Severe Combined Immunodeficiency, or SCID, is a genetic condition that causes impaired development of the immune system. People can develop SCID, as dramatized in the 1976 movie “The Boy in the Plastic Bubble." Other animals can develop SCID, too, including mice.
Researchers in the 1980s recognized that SCID mice could be implanted with human immune cells for further study. Such mice are called “humanized" mice and have been optimized over the past 30 years to study many questions relevant to human health.
Mice are the most commonly used animal in biomedical research, but results from mice often do not translate well to human responses, thanks to differences in metabolism, size and divergent cell functions compared with people.
Nonhuman primates are also used for medical research and are certainly closer stand-ins for humans. But using them for this purpose raises numerous ethical considerations. With these concerns in mind, the National Institutes of Health retired most of its chimpanzees from biomedical research in 2013.
Alternative animal models are in demand.
Swine are a viable option for medical research because of their similarities to humans. And with their widespread commercial use, pigs are met with fewer ethical dilemmas than primates. Upwards of 100 million hogs are slaughtered each year for food in the U.S.
In 2012, groups at Iowa State University and Kansas State University, including Jack Dekkers, an expert in animal breeding and genetics, and Raymond Rowland, a specialist in animal diseases, serendipitously discovered a naturally occurring genetic mutation in pigs that caused SCID. We wondered if we could develop these pigs to create a new biomedical model.
Our group has worked for nearly a decade developing and optimizing SCID pigs for applications in biomedical research. In 2018, we achieved a twofold milestone when working with animal physiologist Jason Ross and his lab. Together we developed a more immunocompromised pig than the original SCID pig – and successfully humanized it, by transferring cultured human immune stem cells into the livers of developing piglets.
During early fetal development, immune cells develop within the liver, providing an opportunity to introduce human cells. We inject human immune stem cells into fetal pig livers using ultrasound imaging as a guide. As the pig fetus develops, the injected human immune stem cells begin to differentiate – or change into other kinds of cells – and spread through the pig's body. Once SCID piglets are born, we can detect human immune cells in their blood, liver, spleen and thymus gland. This humanization is what makes them so valuable for testing new medical treatments.
We have found that human ovarian tumors survive and grow in SCID pigs, giving us an opportunity to study ovarian cancer in a new way. Similarly, because human skin survives on SCID pigs, scientists may be able to develop new treatments for skin burns. Other research possibilities are numerous.
The ultraclean SCID pig biocontainment facility in Ames, Iowa. Adeline Boettcher, CC BY-SA
Pigs in a bubble
Since our pigs lack essential components of their immune system, they are extremely susceptible to infection and require special housing to help reduce exposure to pathogens.
SCID pigs are raised in bubble biocontainment facilities. Positive pressure rooms, which maintain a higher air pressure than the surrounding environment to keep pathogens out, are coupled with highly filtered air and water. All personnel are required to wear full personal protective equipment. We typically have anywhere from two to 15 SCID pigs and breeding animals at a given time. (Our breeding animals do not have SCID, but they are genetic carriers of the mutation, so their offspring may have SCID.)
As with any animal research, ethical considerations are always front and center. All our protocols are approved by Iowa State University's Institutional Animal Care and Use Committee and are in accordance with The National Institutes of Health's Guide for the Care and Use of Laboratory Animals.
Every day, twice a day, our pigs are checked by expert caretakers who monitor their health status and provide engagement. We have veterinarians on call. If any pigs fall ill, and drug or antibiotic intervention does not improve their condition, the animals are humanely euthanized.
Our goal is to continue optimizing our humanized SCID pigs so they can be more readily available for stem cell therapy testing, as well as research in other areas, including cancer. We hope the development of the SCID pig model will pave the way for advancements in therapeutic testing, with the long-term goal of improving human patient outcomes.
Adeline Boettcher earned her research-based Ph.D. working on the SCID project in 2019.
Satellite imagery can help better predict volcanic eruptions by monitoring changes in surface temperature near volcanoes.
- A recent study used data collected by NASA satellites to conduct a statistical analysis of surface temperatures near volcanoes that erupted from 2002 to 2019.
- The results showed that surface temperatures near volcanoes gradually increased in the months and years prior to eruptions.
- The method was able to detect potential eruptions that were not anticipated by other volcano monitoring methods, such as eruptions in Japan in 2014 and Chile in 2015.
How can modern technology help warn us of impending volcanic eruptions?
One promising answer may lie in satellite imagery. In a recent study published in Nature Geoscience, researchers used infrared data collected by NASA satellites to study the conditions near volcanoes in the months and years before they erupted.
The results revealed a pattern: Prior to eruptions, an unusually large amount of heat had been escaping through soil near volcanoes. This diffusion of subterranean heat — which is a byproduct of "large-scale thermal unrest" — could potentially represent a warning sign of future eruptions.
Conceptual model of large-scale thermal unrestCredit: Girona et al.
For the study, the researchers conducted a statistical analysis of changes in surface temperature near volcanoes, using data collected over 16.5 years by NASA's Terra and Aqua satellites. The results showed that eruptions tended to occur around the time when surface temperatures near the volcanoes peaked.
Eruptions were preceded by "subtle but significant long-term (years), large-scale (tens of square kilometres) increases in their radiant heat flux (up to ~1 °C in median radiant temperature)," the researchers wrote. After eruptions, surface temperatures reliably decreased, though the cool-down period took longer for bigger eruptions.
"Volcanoes can experience thermal unrest for several years before eruption," the researchers wrote. "This thermal unrest is dominated by a large-scale phenomenon operating over extensive areas of volcanic edifices, can be an early indicator of volcanic reactivation, can increase prior to different types of eruption and can be tracked through a statistical analysis of little-processed (that is, radiance or radiant temperature) satellite-based remote sensing data with high temporal resolution."
Temporal variations of target volcanoesCredit: Girona et al.
Although using satellites to monitor thermal unrest wouldn't enable scientists to make hyper-specific eruption predictions (like predicting the exact day), it could significantly improve prediction efforts. Seismologists and volcanologists currently use a range of techniques to forecast eruptions, including monitoring for gas emissions, ground deformation, and changes to nearby water channels, to name a few.
Still, none of these techniques have proven completely reliable, both because of the science and the practical barriers (e.g. funding) standing in the way of large-scale monitoring. In 2014, for example, Japan's Mount Ontake suddenly erupted, killing 63 people. It was the nation's deadliest eruption in nearly a century.
In the study, the researchers found that surface temperatures near Mount Ontake had been increasing in the two years prior to the eruption. To date, no other monitoring method has detected "well-defined" warning signs for the 2014 disaster, the researchers noted.
The researchers hope satellite-based infrared monitoring techniques, combined with existing methods, can improve prediction efforts for volcanic eruptions. Volcanic eruptions have killed about 2,000 people since 2000.
"Our findings can open new horizons to better constrain magma–hydrothermal interaction processes, especially when integrated with other datasets, allowing us to explore the thermal budget of volcanoes and anticipate eruptions that are very difficult to forecast through other geophysical/geochemical methods."
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