The ocean was located in the Utopia plain on Mars. how ITAR-TASS reports with reference to a researcher at the Institute Space Research RAS Mikhail Ivanov, now in the field of this the plains can be observed its remains. 
A photo from open sources Photo of the plain Utopia of the Viking-2. © NASA The existence of the ocean is confirmed by mud eddies in Utopia Plain, data from research devices, and the characteristic terrain. Scientists suggest that glaciation of the ocean began during the Hesperian era on Mars, lasting 3.5–2.9 billion years ago. Huge lava fields gradually covered with ice – for this reason glaciation could occur. Ivanov stated that, according to assumptions, during this period on the planet there was a constant hydrosphere, and the ocean in the Utopia region was a rounded pool, formed by a collision with a celestial body. 
A photo from open sources
Plain Utopia – upper right. © NASA Scientists not exclude the fact that in the Hesperian era on Mars could exist and the biosphere: in three Martian meteorites origin were found formations similar to fossils – the remains of microorganisms. Plain Utopia (Utopia Planitia) – 3500 km lowland in the northern hemisphere of Mars. In this sat down a plain lander launched in 1975 space apparatus “Viking-2”. He received and transmitted to the Earth panoraman images as well as conducted soil studies – some the chemicals in it contained sulfur and chlorine like substances that form after the evaporation of sea water.
Mars NASA
