Every Living Thing on Earth Descends from a Single Ancestor—And It’s Much Older Than We Thought

One of the most profound and fascinating questions in science is: How did life begin on Earth?

While our planet is 4.5 billion years old, life didn’t emerge immediately. Instead, it took hundreds of millions of years before the first primitive organisms appeared. Now, a new study conducted by an international team of researchers has unveiled groundbreaking insights into the origins of life, suggesting that the Last Universal Common Ancestor (LUCA) is far older than previously believed.

LUCA: The Common Ancestor of All Life on Earth

LUCA, or the Last Universal Common Ancestor, is the single organism from which all life on Earth—bacteria, plants, animals, and even humans—descended.

This ancient entity was a prokaryotic organism—a simple, single-celled life form without a nucleus—that existed nearly 4 billion years ago. Though primitive, LUCA was capable of reproduction, energy intake, and environmental interaction, laying the foundation for all life forms we see today.

For decades, scientists estimated that LUCA emerged around 3.8 billion years ago, only a few hundred million years after Earth's formation. However, a recent study from the University of Bristol has pushed this timeline back by approximately 400 million years, suggesting that LUCA lived as early as 4.2 billion years ago.

How Did Scientists Determine LUCA’s Age?

To pinpoint the age of LUCA, researchers used a technique known as phylogenetic analysis, which traces genetic evolution across different species.

As organisms evolve, their DNA undergoes mutations, which accumulate over generations. By analyzing these genetic changes—similar to using a "molecular clock"—scientists compared the genes of modern bacteria, plants, and even humans, tracking their divergence from a common ancestor.

Through this process, they concluded that LUCA predates earlier estimates, emerging just a few hundred million years after Earth formed—a timeframe that dramatically reshapes our understanding of life’s origins.

What Did LUCA Look Like?

Although LUCA left behind no fossils, scientists have reconstructed its likely characteristics based on the shared genetic traits of modern organisms.

Despite its simplicity, LUCA was more advanced than previously thought. Researchers believe it may have possessed a primitive immune system, capable of defending itself against viruses and other environmental threats—a surprising level of complexity for such an early life form.

LUCA likely thrived in a water-rich, mineral-laden environment under extreme temperatures and pressures, possibly near hydrothermal vents deep in Earth's oceans. It also wasn’t alone—scientists suspect it was part of a primitive ecosystem, in which its metabolic waste supported other microbial life, setting the stage for Earth’s first natural recycling system.

A Window Into Our Evolutionary Past

By pushing LUCA’s origin back to 4.2 billion years ago, this research offers crucial new insights into the emergence of life on Earth. LUCA was not just a single cell—it was the foundation of a vast and diverse web of life that has been evolving for billions of years.

The findings also highlight the importance of genetics and evolutionary studies in uncovering our biological history. But even with this discovery, many questions remain—perhaps the biggest being: How did LUCA come into existence?

Theories like the "primordial soup" hypothesis or the idea that life originated in deep-sea hydrothermal vents offer potential explanations, but no single theory has been definitively proven.

What is certain, however, is that LUCA played a pivotal role in shaping the course of life on Earth. Every organism—from the simplest bacteria to modern humans—can trace its lineage back to this ancient ancestor.