Some 4.2 billion years ago, Earth was a hostile world of searing volcanoes and constant asteroid strikes. Yet in that chaos, scientists now believe our Last Universal Common Ancestor (LUCA) was already alive, thriving only a few hundred million years after the planet formed. LUCA was not the very first life, but the ancient ancestor from which every organism, bacteria, trees, whales, and humans, ultimately descends.⁠ ⁠ By comparing the genomes of hundreds of microbes, researchers reconstructed LUCA’s traits. Far from a primitive spark, this single-celled organism was surprisingly sophisticated. Its genome likely encoded around 2,600 proteins, and it fueled itself with hydrogen and carbon dioxide. Even more striking, LUCA appears to have carried a rudimentary immune system, an early CRISPR-like defense, showing that even at this primordial stage, viruses were already a force shaping life.⁠ ⁠ The findings place LUCA in the Hadean Eon, a time once thought too extreme for biology. With Ear...