Sadly our presence in the ocean depths isn't as transient as we may wish, with pollution in the Mariana Trench. https://www.theguardian.com/environment/2018/dec

Sadly our presence in the ocean depths isn't as transient as we may wish, with pollution in the Mariana Trench. https://www.theguardian.com/environment/2018/dec/20/plastic-pollution-mariana-trench-deepest-point-ocean https://www.theguardian.com/environment/2018/dec/20/plastic-... Perhaps we will detect the traces of alien life by what they discard, which is what some suggested 'Oumuamua could be.