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Earth, a planetary PCR machine, a new hypothesis on the origin of life

Juan Jiménez proPOSES hat the thermal cycles of the planet could have driven the formation of the first living molecules

This new theory represents a new framework for understanding and research on the transition from a chemical planet to a living planet

How did life arise on Earth? What conditions allowed simple chemical compounds to transform into molecules capable of replication and evolution? In a new theory published in the journal Discover Life, Pablo de Olavide University Professor of Genetics Juan Jiménez proposes that the planet itself functioned as a giant natural “PCR machine”, thanks to the thermal cycles of day and night.

PCR (Polymerase Chain Reaction) is a laboratory technique that replicates DNA fragments through temperature variations. Jiménez suggests that, more than 4 billion years ago, thermal oscillations in the Earth's environment could have triggered similar reactions, allowing nucleotides - the basic building blocks of RNA - to join together to form stable molecular structures.

“The cold at night could have temporarily held two nucleotides together by hydrogen bridging. With the arrival of daylight, solar heat would have provided them with the energy needed to bind stably through covalent (permanent) bonds, thus initiating a first chain of two links,” explains Jiménez. Metaphorically, he compares this moment with the famous image of Michelangelo's 'The Creation of Adam' in the Sistine Chapel: “The union of these two nucleotides is reminiscent of the contact between the fingers of God and Adam, like the spark that created life”.



The contact in Michelangelo's work intuitively represents the origin of the human being. As a metaphor, the contact of two nucleotides could represent the beginning of life.

The hypothesis focuses on a fundamental molecule: transfer RNA, essential in ribosomes to produce proteins. For Jiménez, its clover-shaped structure is a “molecular fossil” that could have arisen from a simple RNA hairpin, generated in those early thermal cycles. “These initial hairpins could not only replicate, but also begin to encode proteins long before complete cells existed, such as LUCA (Last Universal Common Ancestor) from which all living things we know today evolved,” he says.

The researcher also takes up an idea put forward by Darwin, who proposed that life could have originated in a small pool rich in organic compounds, the so-called “primordial soup”. Jiménez updates this idea by suggesting that this environment could have been a lagoon formed by the impact of a meteorite rich in organic molecules, like the present-day craters of Wolf Creek (Australia) or Lonar (India). “That pond would have functioned as the well of a planetary PCR, generating the first RNA hairpins under natural conditions,” he says.



Temperature cycling makes the earth a thermocycling machine theoretically capable of forming and replicating RNA hairpins.

Jiménez, who carries out his research work at the Andalusian Center for Developmental Biology (CABD - joint center of CSIC, UPO and Junta de Andalucía), raises the possibility that hydrophobic amino acids from those first RNA-protein complexes could have also added fatty acids present in the soup and that, after a selective process of some tens (perhaps hundreds) of millions of years, these lipid-wrapped aggregates could have derived into the first 'LUCA' cell, a self-sufficient biological unit capable of leaving the primordial soup to colonize the planet.

 Reference:

Jiménez, J. (2025). Earth, a planetary PCR machine to create life, or the brief history of a tRNA. Discover Life 55, 17. 2025. https://doi.org/10.1007/s11084-025-09691-8

Podcast: https://www.youtube.com/watch?v=jbKPXyXbi-g

A permanent lake caused by a meteorite/comet impact could have acted as a primordial soup subject to strong daily temperature fluctuations.

This press release was made in collaboration with the UPO Communication Unit.