Quotation source : http://en.wikipedia.org/wiki/Life_on_Mars
The ALH84001 meteorite was found in December 1984 in Antarctica, by members of the ANSMET project; the meteorite weighs 1.93 kilograms (4.3 lb). The sample was ejected from Mars about 17 million years ago and spent 11,000 years in or on the Antarctic ice sheets. Composition analysis by NASA revealed a kind of magnetite that on Earth, is only found in association with certain microorganisms. Then, in August 2002, another NASA team led by Thomas-Keptra published a study indicating that 25% of the magnetite in ALH 84001 occurs as small, uniform-sized crystals that, on Earth, is associated only with biologic activity, and that the remainder of the material appears to be normal inorganic magnetite. The extraction technique did not permit determination as to whether the possibly biological magnetite was organized into chains as would be expected.
In November 2009, NASA scientists reported after more detailed analyses, that a biogenic explanation is a more viable hypothesis for the origin of the magnetites in the meteorite.
The Nakhla meteorite fell on Earth on June 28, 1911 on the locality of Nakhla, Alexandria, Egypt.
In 1998, a team from NASA's Johnson Space Center obtained a small sample for analysis. Researchers found preterrestrial aqueous alteration phases and objects of the size and shape consistent with Earthly fossilized nanobacteria, but the existence of nanobacteria itself is controversial. Analysis with gas chromatography and mass spectrometry (GC-MS) studied its high molecular weight polycyclic aromatic hydrocarbons in 2000, and NASA scientists concluded that as much as 75% of the organic matter in Nakhla "may not be recent terrestrial contamination".
You may also refer this link to get a detailed explanation of documented evidences of life outside earth.
There is also a popular hypothesis exists that even life on earth started by a meteor or asteroid which landed on earth. Bacteria and viruses are known to survive extreme temperatures and vacuum.
The kepler probe data and various other data exists that there are planets like earth. There hasn't been a solid proof that we are not alone. But there are various signs and much more like above. There are many solar systems and many other universes, which CAN support life. Let's wait if anyone visits us.