Page 25 - (DK) Eyewitness - Mars

Hesperian Age

The Hesperian era lasted from about 3.5
billion years ago to 2.5 billion years ago.
Volcanoes rumbled and lava flowed, but
volcanic activity slowed down as Mars
cooled. Water began freezing, forming ice
on the surface and underground. In this
time of change, there were probably
torrential flash floods, which cut deep, wide
channels. As water retreated underground
and froze, Mars became drier, making a
transition to another age.

AN AGE OF VOLCANOES
This illustration shows a Hesperian-era volcano in
majestic eruption, sending smoke and ash into the sky.
Such volcanic activity could have melted underground
ice, causing floodwaters to suddenly burst out and
scour deep channels in the Martian surface.

The Amazonian Age

The Amazonian era began about 2.5 billion years ago and extends to
the present. During this period cratering and volcanic eruptions have
continued but at lower levels than in previous ages. Today, Mars is dry
and dusty, with a very thin atmosphere. One reason for this dryness is
that atmospheric pressure is now so low that water reaching the surface
freezes immediately or boils away. In this, the Amazonian Age, most of
the water remaining on Mars is in the form of underground ice.

MARTIAN ROCK ON EARTH
This meteorite was discovered near Los
Angeles in the 1970s. Scientific analysis
found it originated on Mars. It is composed
of lava and weighs just under a pound
(452.6 g). It is only 175 million years old,
proving that Martian volcanoes have been
active in recent Amazonian times.
YOUTHFUL LOWLANDS
West of the Tharsis volcanic region is the low-lying
Amazonis Planitia, which gives its name to the Amazonian
Age. This photograph shows the lava-covered surface of the
planitia, where fewer impact craters are found than in the
older upland regions.