It is also possible that life existed on Venus but not anymore. Assuming the process that delivered water to Earth was common to all the planets near the habitable zone, it has been estimated that liquid water could have existed on its surface for up to 600 million years during and shortly after the Late Heavy Bombardment, which could be enough time for simple life to form, but this figure can vary from as little as a few million years to as much as few billion.[15][16][17][18][19] This might also have given enough time for microbial life to evolve to be aerial.[20] There has been very little analysis of Venusian surface material, so it is possible that evidence of past life, if it ever existed, could be easy to find with a probe capable of surviving Venus's current atmospheric conditions.[6][21]