Before revision: During past ages, there was rain and snow on Mars ; especially in the Noachian and early Hesperian epochs.Baker, V. R. (1982), The Channels of Mars, 198 pp., Univ.
After revision: Rain and snow was a regular occurrence on Mars in the past ; especially in the Noachian and early Hesperian epochs.Baker, V. R. (1982), The Channels of Mars, 198 pp., Univ.