The Curiosity rover was designed to assess whether Mars ever had an environment able to support small life forms called microbes. In other words, its mission is to determine the planet's "habitability."

To try to solve this question, the rover analyzes samples scooped from the soil and drilled from rocks. The record of the planet's climate and geology is essentially "written in the rocks and soil" -- in their formation, structure, and chemical composition. The rover's onboard laboratory will study rocks, soils, and the local geologic setting in order to detect chemical building blocks of life (e.g., forms of carbon) on Mars and will assess what the martian environment was like in the past.

So far, the rover has not found direct evidence that life has ever existed on Mars. But the rover did analyze rock from an ancient lake on Mars and discovered that it contained molecules containing carbon and nitrogen that are useable to lifeforms.

This is not evidence that life existed, but it may suggest that at one point, the environment on Mars was capable of sustaining life – which means that it is worthwhile to keep studying Mars and looking for signs of past life.

Check out this video link below to see a NASA scientist talk about the rover’s biggest accomplishments since it landed on Mars over 3 years ago!

No, not yet. Any life on Mars is probably going to be microscopic, which means that our current rovers won't be able to find it with the tools that they have. We're going to need new rovers.