Hunting the First

Listen to Today's Edition:

There weren’t always billions of humans and trillions of plants, animals and fungi thriving on Earth, which implies that going far enough up the genealogical tree, one could find the ancestor of all living things.

The search for what scientists call the “last universal common ancestor” (LUCA) has been the subject of debate among researchers over what it was, and when it emerged.

Now, a team of scientists from the University of Bristol has established that the LUCA could be at least 4.2 billion years old, thus appearing at the very early stages of our planet’s existence – Earth was formed 4.5 billion years ago.

“We did not expect the LUCA to be so old, within just hundreds of millions of years of Earth’s formation,” said study co-author Sandra Alvarez-Carretero.

Back then, Earth was still a toxic environment. Oxygen only emerged 3 billion years ago, but life was already possible before that, as modern scientists believe our planet was stable enough.

The LUCA gave us and our Earth-mates the same amino acids to build proteins, the same energy currency, ATP, and the fact of using DNA to store information. Carretero and her colleagues counted the number of mutations in species to determine when our more recent ancestors diverged from the LUCA.

Then, thanks to complex evolutionary modeling, the researchers found that the LUCA was probably a prokaryote – a single-celled organism without a nucleus.

“(The) LUCA was a complex organism, not too different from modern prokaryotes,” said co-author Davide Pisani. It also had an early immune system to combat viruses.

The LUCA, in fact, evolved in an environment full of life: Its waste could have fed other lifeforms.

This “demonstrates just how quickly an ecosystem was established on early Earth,” said co-author Philip Donoghue. “This suggests that life may be flourishing on Earth-like biospheres elsewhere in the Universe.”