"-A pair of astrophysicists studying gamma ray bursts has found that such events might play a much larger role in the existence of life on Earth and other planets than has been thought."
Among other things, they found that based on the likely average incidence of GRBs happening close enough, calculations showed a 60 percent likelihood that a GRB has caused an extinction event here on Earth within just the past billion years. They also found that planets are likely to be less impacted by GRBs the farther away from the center of their galaxy they are simply because there are less such events occurring due to the existence of fewer stars in general. They also noted that it appears unlikely any form of life would have been able to survive anywhere in the known universe prior to 5 billion years ago, as galaxies were so compact before then and strikes would have been very common.
So, all life in the univers might only had appear 5 billion years ago. If there are life elsewhere in the univers it could not be a lot older then here on earth (May be younger if earth life appear soon). If all civilisation are about the same age, then we might be among the first one and contact between civilisation is rare because civilisation are rare for now. Just a thought.
http://arxiv.org/abs/1409.2506
http://dx.doi.org/10.1103/PhysRevLett.113.231102