To emphasize the great size of the volume of water that seems to have flowed through Mars’ outflow channels

To indicate data used by scientists to estimate how long ago Mars’ outflow channels were formed

To argue that flash floods on Mars may have been powerful enough to cause tear-shaped “islands” to form

To argue that the force of flood waters on Mars was powerful enough to shape the northern volcanic plains

They formed at around the same time that volcanic activity was occurring on the northern plains

They are found only on certain parts of the Martian surface

They sometimes empty onto what appear to have once been the wet sands of tidal beaches

They are thought to have carried water northward from the equatorial regions

What are some regions of Mars that may have once been covered with an ocean?

Where do mission scientists believe that the river forming the delta emptied?

Approximately how many craters on Mars do mission scientists believe may once have been lakes filled with water?

During what period of Mars’ history do some scientists think it may have had large bodies of water?

the polar regions of Mars were once more extensive than they are now

a large part of the northern lowlands may once have been under water

deltas were once a common feature of the Martian landscape

the shape of the Hellas Basin has changed considerably over time

If ancient oceans ever existed on Mars’ surface, it is likely that the water in them has evaporated by now

If there is any liquid water at all on Mars’ surface today, its quantity is much smaller than the amount that likely existed there in the past

Small-scale gullies on Mars provide convincing evidence that liquid water existed on Mars in the recent past

The small amount of water vapor in the Martian atmosphere suggests that there has never been liquid water on Mars

Ancient oceans on Mars contained only small amounts of carbon

The climate of Mars may not have been suitable for the formation of large bodies of water

Liquid water may have existed on some parts of Mars’ surface for long periods of time

The ancient oceans that formed on Mars dried up during periods of cold, dry weather

clues

features

arguments

effects