Science

In what may one day be remembered as a defining moment in our search for life beyond Earth, astronomers have uncovered compelling evidence of biological signatures on a faraway exoplanet — signs that, until now, have only ever been associated with living organisms on our own planet.

The discovery centers on K2-18b, an ocean-rich world orbiting a red dwarf star in the Leo constellation, approximately 124 light-years from Earth. What makes this planet particularly intriguing is not just its Earth-like temperature or its position in the so-called “habitable zone”, but what its atmosphere is telling us.

Using the ultra-sensitive instruments aboard the James Webb Space Telescope (JWST), a team of scientists led by Professor Nikku Madhusudhan from the University of Cambridge has detected dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) — two sulfur-based compounds that, here on Earth, are almost exclusively produced by marine microorganisms, particularly phytoplankton.

These chemical signatures were found in concentrations thousands of times stronger than those typically present in Earth’s atmosphere — a detail that suggests something extraordinary may be occurring on K2-18b.

The implications? As per current scientific understanding, no known non-biological processes produce these molecules in such abundance. The team believes that the presence of an ocean beneath the exoplanet’s hydrogen-rich atmosphere, combined with these molecules, strengthens the case for a thriving microbial biosphere — or at the very least, complex chemical activity mimicking biological processes.

To put it simply, this is the most compelling evidence yet for potential life outside our solar system.

While these claims are not yet definitive proof of life, the findings represent a major step forward. The signals have reached a “three-sigma” level of statistical significance, which means there is just a 0.3% chance the detection happened randomly. Scientists are aiming for the more stringent five-sigma threshold to confirm it as a bona fide scientific discovery, for which they estimate another 16 to 24 hours of JWST observation time would suffice.

The atmosphere of K2-18b had already shown traces of methane and carbon dioxide in previous observations — key carbon-based molecules needed for life. Now, the independent detection of DMS and DMDS using a different JWST instrument in a separate wavelength range only deepens the mystery.

“We’ve reached a moment where the idea of a living universe no longer feels out of reach,” says Professor Madhusudhan. “This is the closest we’ve ever come to spotting the potential chemical footprints of life on another world.”

His team remains cautious, acknowledging that unknown chemical processes could also be at play. They are now working to determine whether the detected molecules could be produced abiotically, without the involvement of life.

And it’s not just K2-18b that’s raising eyebrows in the cosmic neighborhood.

In a separate breakthrough, scientists examining Martian rock samples have discovered organic molecules of unprecedented length — carbon chains up to 12 atoms long. These structures, found in rocks billions of years old, are often associated with fatty acids, key components of fats and oils that arise from biological activity on Earth.

Together, these two discoveries — on K2-18b and Mars — are fueling renewed excitement about the age-old question: Are we alone?

While we may still be a few steps away from a definitive answer, the path to it has never been clearer.

As more data pours in and telescope capabilities expand, the cosmos may finally begin to whisper its deepest secret — that life, in some form, may not be a rare miracle, but a universal truth.

For decades, scientists believed that intelligent life, like humans, was an incredibly rare fluke—an outcome so unlikely that it may have happened only once in the vast universe. The prevailing view, supported by some of the greatest evolutionary biologists and theoretical physicists, was that the emergence of complex life required an improbable sequence of evolutionary leaps, known as hard steps.

However, new research challenges this idea. A growing number of scientists now argue that the evolution of humanlike intelligence was not just a stroke of cosmic luck but rather an expected outcome of Earth’s long and complex history. Could it be that intelligent life is not as rare as we once thought?

The Hard-Steps Hypothesis: A Cosmic Coincidence?

In 1983, physicist Brandon Carter attempted to explain why intelligent life emerged within Earth’s 5-billion-year history. He dismissed the idea that intelligence arises quickly, as it took billions of years on Earth. He also rejected the possibility that evolution and the Sun’s lifespan coincidentally operate on similar timescales. Instead, he concluded that intelligent life is incredibly rare, requiring a series of unlikely hard steps, each with an extremely low probability of occurring.

Carter’s model suggests that Earth was extraordinarily lucky, as these crucial evolutionary steps would usually take trillions of years—far beyond the lifespan of most stars.

Some of the most widely recognized hard steps include:

• The origin of life
• The emergence of eukaryotic (nucleated) cells
• The development of oxygen-producing photosynthesis
• The evolution of multicellular organisms
• The rise of humanlike intelligence

If these steps were truly improbable, they should have occurred only once in Earth’s history. And according to traditional interpretations of the fossil record, that’s exactly what happened.

But is that really the case?

Did Evolutionary Hard Steps Happen More Than Once?

While the hard-steps model has long been accepted, paleontologist Geerat Vermeij proposed an alternative explanation. He argued that these so-called rare evolutionary leaps might have happened multiple times, but we just don’t have the evidence to prove it.

Why Would Evidence Be Missing?

1. Extinction & Fossil Gaps – Many ancient species may have gone extinct before leaving a fossil record, making it seem like key evolutionary breakthroughs happened only once.
2. Competition & Environmental Change – When a species undergoes a major evolutionary innovation, it may outcompete other species that were evolving toward the same breakthrough, wiping them out before they could establish themselves.
3. Environmental Constraints – Some conditions may have allowed only a single lineage to develop a particular trait, making it appear unique.

If these explanations hold true, then the hard steps weren’t truly hard—they were simply unique events shaped by environmental factors.

Why Didn’t Intelligence Emerge Sooner?

If the evolution of intelligence wasn’t as improbable as Carter suggested, then why didn’t it happen much earlier? The answer may lie not in biology, but in Earth’s changing environment.

Earth’s Long Road to Habitability

• Oxygen Scarcity – For nearly 90% of Earth’s history, oxygen levels were too low to support complex life, delaying the rise of intelligent beings.
• Eukaryotic Cells Needed Oxygen – It took nearly 50% of Earth’s history before there was enough oxygen for eukaryotic (complex) cells to thrive.
• Environmental Complexity Grew Over Time – As Earth’s climate, oceans, and atmosphere evolved, new ecological niches emerged, allowing for greater biological complexity.

Rather than being a sequence of lucky accidents, the emergence of intelligence may have been a natural response to Earth’s changing conditions. Humans arose when they did because Earth only recently became capable of supporting them.

What This Means for the Search for Alien Intelligence

If intelligence was an inevitable outcome of Earth’s evolution, could the same be true on other planets?

To test this theory, scientists from multiple disciplines—from microbiology and paleontology to astrophysics—are collaborating to understand how life co-evolves with planetary environments.

Key Questions Moving Forward

• Are “hard steps” truly rare, or did they happen multiple times in Earth’s history?
• How long will Earth remain habitable for humanlike intelligence?
• How common are life-friendly planets with conditions similar to Earth’s?
• Do planets outside our solar system show evidence of key evolutionary milestones, like oxygen-producing photosynthesis?

If these studies confirm that Earth’s evolutionary pathway is typical rather than extraordinary, then the universe may be filled with intelligent life waiting to be discovered. The hard-steps model may have overestimated how difficult it is for life to develop, making extraterrestrial intelligence far more likely than we once believed.

The search for alien civilizations may have just become a lot more promising.

Conclusion: Was Human Intelligence Inevitable?

New research suggests that intelligent life may not be as rare as once thought. Instead of being an improbable cosmic accident, the rise of humans could be a predictable outcome of a planet evolving over billions of years.

This revolutionary perspective shifts how we think about our place in the universe. If intelligence is a natural consequence of planetary evolution, then somewhere out there, other civilizations may already exist—or may be just on the verge of emerging.

The only question now is: Are we alone? Or are we just the first to find out?