Question 1
Multiple choiceMedium1 markA study finds the same genetic code and shared genes across bacteria, archaea and eukaryotes. The oldest known fossil evidence of cells is dated to 3.5 billion years ago, while a molecular-clock estimate places LUCA at 3.8 billion years ago. Which interpretation is supported?
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Answer: B. A universal genetic code and genes shared across the three domains support common ancestry and LUCA. A molecular clock estimates LUCA’s age, while fossils provide evidence that cells existed by the fossil date, not the exact beginning of life. Earlier lineages could have become extinct through competition with LUCA and its descendants. A: Treats the oldest known fossil as the exact origin of life; fossil evidence does not establish that life began then. C: Reverses the dating approaches: molecular clocks estimate LUCA’s age, while fossils provide evidence of ancient cells. D: Equates LUCA with the first life and treats its estimated age as excluding earlier forms. Remember: LUCA is the latest common ancestor of extant life, not necessarily the first life.