. >> reporter: tim farley leads the team that will direct the team through the area. >> the oldest evidenceold. the rocks were deposited in a shallow sea. this crater that you see here was a lake 3.5 billion years ago so we are looking at the same environment and the same time period, two different planets. >> it's determined however long in the future that know there was not ever life, what does that mean? >> the place where perseverance landed here is the most habitable time period in mars and the most habitable environment we know about. this is as good as it gets at least of our current understanding of what we understand. if we don't find life here, it makes us worry perhaps it doesn't exist anywhere. >> perseverance's telescopic camera spotted a lot of boulders he didn't expect to see in the middle of an ancient lake. >> so this is surprising? >> absolutely. >> what do those boulders tell new. >> the most reasonable interpretation tell you the flood. you don't have fast flowing water in the middle of a lake. you get fast flowing water in the river. there was a river that was capable o