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[ whoosh ]

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In 2012 NASA's Curiosity rover
went to Mars

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to explore Gale Crater,

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a large impact basin

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with a massive, layered
mountain in the middle.

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How did this strange
landscape come to be?

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And what can its
history teach us

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about the potential
for life on Mars?

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After several years of
exploration,

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here's what we think
could have happened.

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A Guide to Gale Crater

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Around 3.7 billion years ago

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a large meteor impact blasts out
the initial crater,

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[ boom ]

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cracking the rock below and
leaving a central peak

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as the surface rebounds.

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It's a wetter time
in Mars' history.

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Groundwater seeps into
the new crater,

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while rivers fed by rain or
melting snow also flow in,

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forming a large lake--

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and carrying in gravel,
sand and silt.

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This material keeps building up
over millions of years.

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And as each layer
cements into rock,

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it records a snapshot of the
environment that shaped it.

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In time, the gradual drying
of Mars shuts off the rivers.

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But sediment keeps piling up

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as sand and dust blow
into the crater,

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deeply burying the deposits
laid down in water.

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Meanwhile, groundwater remains
deep below the dusty surface.

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At some point, winds that
once carried sediment in

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begin scouring it back out.

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In areas closer to
the crater rim

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these winds dig all the way down
into the ancient lake deposits.

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And as the heavy weight above is
lifted, these layers crack,

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which helps groundwater flow
through and alter them again

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before they dry out.

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By about 3 billion years ago,

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we're left with the basic form
we see today.

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It's in this version
of Gale Crater

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that Curiosity has helped
piece together the story.

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Sediment patterns show a
lot of water was present,

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continually, over many
millions of years--

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both as persistent groundwater
and a long-standing lake

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(with occasional dry spells).

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Mineral and chemical
readings show

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that water from both the
lake and subsurface

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was friendly for
potential microbes.

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Drill samples from the lakebed
show key elements,

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organic molecules, nutrients
and energy sources

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that microbes could have used.

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Water flowing through
underground fractures

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could have supported life
even in deeply buried rocks.

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And the composition of
some layers makes them

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good for preserving potential
signs of past life.

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Taken together, the evidence
points to Gale Crater

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(and Mars in general)

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as a place where life
--if it ever arose--

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might have survived
for some time.

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With our primary mission
fulfilled,

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we continue exploring:
uncovering the history of Mars

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and learning more abut how and
where future missions

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can search for the signatures
that ancient life

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may have left behind.

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NASA Jet Propulsion Laboratory