Astronomers have detected the presence of phosphine in the atmosphere of Venus. This could indicate the presence of life since some living organisms are known to produce phosphine. There is a reason to be careful because the chemical can also be made in another way. This is not conclusive proof of life on Venus, but it is certainly exciting news and worthy of further investigation. But suppose for a moment that it is produced by life on Venus. If so, it could be terrible news for life on Earth.

The question of whether life is abundant in the universe remains one of the great cosmic mysteries. From the evidence we have, we know that all the ingredients necessary for life are common. Most stars have planets and countless worlds orbiting the living area of their star. The building blocks of life as we know it are also found throughout the cosmos. We have found amino acids in meteorites, and can detect them in interstellar clouds of gas and dust. But as for life itself, we still found conclusive evidence.

We also found no evidence of intelligent life beyond Earth. Since life could be cosmically abundant, why not? This is known as the Fermi Paradox and gave rise to many ideas. The first is that bright aliens keep us isolated in some sort of cosmic zoo. They will not reveal themselves until we prove ourselves worthy, which could be a very long time considering the state of our planet.

the Zoo hypothesis sounds a bit like circular reasoning. The fact that we don’t see any strangers is taken as proof that they are there. A better idea is something known as Large filter. First proposed by Robin Hanson, the argument is that while life often occurs in the universe, there is a stage in the evolution of life that is extremely difficult. Single-celled organisms may be easy, but multicellular organisms are difficult, so life rarely exceeds bacteria. It may be that the Cambrian explosion of diverse life rarely occurs. It could also be that young civilizations usually destroy themselves, which is why a benevolent alien species did not visit us.

So what does this have to do with Venusian life and the future of Earth? If cellular life exists on Venus, it implies that it exists almost everywhere. Venus is a hot, inhospitable world that has no liquid water and rains sulfuric acid. If life can evolve in the atmosphere of Venus, then places like Mars, Europe, and Titan almost certainly have life. This means that the right filter does not happen at an early stage.

The big filter has to arrive much later. While Earth has experienced many periods of mass extinctions, life has always bounced back. When it does, it tends to increase its diversity quite quickly. Smart life also seems to offer many opportunities. If we primates had not become civilized, it is likely that another branch of the evolutionary tree would have. If there is life on Venus, then a humid temperate world like Earth will almost certainly give birth to an intelligent species.

But we don’t see intelligent life scattered around the universe. This would likely mean that the great filter occurs after the rise of civilization. Here on Earth, we now have the technological power to transform our environment. But our technology has also created pollution and global warming problems that threaten to lead us to extinction. We could be our own big filter.

It could also be that there is no large filter, and the Fermi paradox has another solution. But as we seek life on neighboring worlds, perhaps we should also take a closer look at the long-term prospects of our world.

Reference: Jane S. Greaves et al. “Phosphine gas in the cloud bridges of Venus.” Nature astronomy Flight. 4, no. 9, (2020).