Researchers reconstruct proteins from ancient bacteria to measure the Earth’s temperature over the ages. The scientists determined that the Earth endured a massive cooling period between 500 million and 3.5 billion years ago. The team wanted to measure Earth’s temperature billions of years ago to learn more about life on Earth during the Precambrian period. But instead of taking the traditional route — analyzing rock formations or measuring isotopes in fossils — they opted to do what they knew best: protein reconstruction.