  Oxygen ($O_2$) is one of the most important elements required to sustain
life. The concentration of $O_2$ on Earth has been accumulated over millions of
years and has a direct connection with that of $CO_2$. Further, $CO_2$ plays an
important role in many other planetary atmospheres. Therefore, molecular
reactions involving $CO_2$ are critical for studying the atmospheres of such
planets. Existing studies on the dissociation of $CO_2$ are exclusively focused
on the C--O bond breakage. Here we report first experiments on the direct
observation of molecular Oxygen formation from $CO_2$ in strong laser fields
with a reaction microscope. Our accompanying simulations suggest that $CO_2$
molecules may undergo bending motion during and after strong-field ionization
which supports the molecular Oxygen formation process. The observation of the
molecular Oxygen formation from $CO_2$ may trigger further experimental and
theoretical studies on such processes with laser pulses, and provide hints in
studies of the $O_2$ and $CO_2^+$ abundance in $CO_2$-dominated planetary
atmospheres.
