Imagine the tree of life. The tip of every branch represents one species, and if you follow any two branches back through time, you'll hit an intersection. If you keep going back in time, you'll eventually find the common ancestor for all of life. That ancestor is called LUCA, the last universal common ancestor, and there is no fossil record to tell us what it looked like.

Luckily, we have Jonathan Lambert. He's a science correspondent for NPR and today he's talking all things LUCA: What we think this single-celled organism may have looked like, when it lived and why a recent study suggests it could be older and more complex than scientists thought.

Have other questions about ancient biology? Email us at [email protected] — we'd love to hear from you!

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In a previous version of this episode, we said that the research team used carbon-dated fossils to calibrate a molecular clock aimed at estimating the age of LUCA. In fact, the researchers used radio isotopic-dated fossils for that purpose.

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