Photosynthetic organisms transform light energy into chemical energy – this process is essential as it is placed at the base of the food chain. Life on Earth has gone through different stages, and the biosphere has changed though these stages. For intelligent life, multicellular organisms with a nervous system are essential (they have a brain), but this took a very long time. To put this in perspective, early forms of photosynthesis evolved around 3.5 billion year ago, and complex life (animals) evolved around 600 million year ago. The right conditions for complex life to evolve were possible once we had our modern Earth System – this happened once plankton colonised the oceans around 800-600 million year ago. In my opinion, getting this stage is the hardest, because you need oceans, photosynthesis and geological processes to producer oxygen and enough bioavailable nitrogen (in addition to sugars produced by the photosynthesis). If we find these sort of conditions, we can find complex life. Now to get to intelligent life, we need time which in our planet this took about 500 million years.
“But, yes if we evolved in this planet, it is possible that intelligent life evolved in another part of the universe,” Sanchez-Baracaldo – Guardian, June 2020
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