Moon and Mars

Earth’s geologic history is divided into several eras. Today, we’re in the Cenozoic era, which began about 66 million years ago.

The current geologic era on Mars has been going on a lot longer. Known as the Amazonian period, it’s been underway for three billion years. That means that not much has changed on the planet during that time.

During earlier eras, the Martian surface changed quickly. Rivers flowed across the landscape, carving channels and canyons. They filled lakes and seas, and perhaps even an ocean. There was a lot of volcanic activity as well.

By the start of the Amazonian, though, things were slowing down. Mars had cooled off, so some of its water froze. But much of the water escaped into space, because Mars’s weak gravity couldn’t hold on to the planet’s atmosphere. Without an atmosphere, standing water vaporized, water molecules were split apart by sunlight, and the hydrogen in the water was whisked away by the solar wind.

That doesn’t mean things have been static over that period, though. Volcanic activity continued, and winds in the thin atmosphere sculpted the landscape — a process that’s still going on. Yet Mars is much quieter than it was during its youth — a world little changed over most of its long history.

And Mars is in good view at dawn tomorrow. It stands to the right of the crescent Moon, and looks like a moderately bright star. The much brighter planet Venus stands below them. More about that tomorrow.

Script by Damond Benningfield