No alien life needed: Dark streaks in Venus' atmosphere can be explained by iron minerals  

 The dark streaks in Venus' atmosphere — a potential sign of life, according to some researchers — can be explained by Iron-bearing sulfate minerals, a new study reports. 

https://cdn.mos.cms.futurecdn.net/Uq3duqeiWqg9QEVAVsj5Xh.jpg

https://www.space.com/dark-streaks-venus-atmosphere-iron-minerals-not-microbes