What evidence did the rovers Spirit and Opportunity find regarding Mars?

The evidence that rovers Spirit and Opportunity found regarding Mars strongly indicates that there was once water on the planet. These rovers discovered various geological formations that resemble those created by water erosion and sediment deposition, such as rock layers, mineral deposits, and hematite spheres, which suggest the historical presence of liquid water. The significance of finding evidence of water is profound because water is a key ingredient for life as we understand it, and the presence of water on Mars in the past raises important questions about the planet's habitability and potential for supporting life.

The other options, while interesting, are not supported by the findings of Spirit and Opportunity. For instance, while the presence of water hints at potential life, no direct evidence of life or bacteria has been discovered. Similarly, there are no signs nor evidence suggesting that petroleum was ever present on Mars, as the geological and environmental conditions on the planet differ greatly from those that lead to petroleum formation on Earth.