The “examples of former life on the Red Planet” were found by alien chasers in images of the Martian surface taken by the NASA Curiosity Rover, which is exploring the planet.
The images are beamed back to Earth and then placed on line by NASA for anyone to view.
The alleged tree stump was shown in a video by YouTube channel Paranormal Crucible.
In a promotional blurb for the video, the channel, which believes it has found other examples of life in similar pictures, said: “Intriguing object found by the Curiosity rover, this time a possible tree stump.
“This object definitely looks out of place and in my opinion could be the petrified remnants of a Martian tree.
“Object is around three feet in height, and with numerous discoveries of plant and animal life on Mars, it would be logical to assume, that a variety of tree either existed, or still exists on this enigmatic planet.”
The video was highlighted by Scott C Waring, editor of ufosightingsdaily.com.
He said: “Paranormal Crucible makes a hypothesis that this could be an ancient tree stump on Mars.
“It’s a good assumption since NASA said Mars was Earth-like when a solar explosion hit the planet, striping the atmosphere and oceans from its surface.”
Mr Waring has been doing his own scouring through Curiosity images and claims to have found a possible alien skull.
He blogged: “Here is an alien skull I found in a Mars photo.
“This skull has dark lines around the eye sockets, just as humans do.
“It has two eye sockets, just as humans do.
“Its nose and mouth area seem to be connected.
“There are two long bones on each side of the mouth area, which could have been part of the jaw area.
“Near the eye socket is a curved bone area on the side of its head, as some human skulls have.
“I have found many skulls on Mars and this one seems similar to a few of them.
“It is 100 per cent evidence that aliens lived and died on Mars long ago.
“Now, if NASA would just do their job, maybe the public can learn about this.”
So have they just uncovered evidence of life on Mars that NASA just won’t tell us about.
Scientists and NASA say these “anomalies” in pictures are just odd-shaped rocks.
They say Mr Waring and colleagues are experiencing the effects of pareidolia – when the brain tricks the eyes into seeing familiar objects or shapes, such as faces or animals in textures or patterns like clouds or the surface of a rock.
Coupled with an over-active imagination, people will see what they want to see.
NASA says it has found no evidence of current or former life on Mars.
However, it has found traces of water beneath the surface and says the planet was once covered in great oceans like Earth.
It believes there could be simple forms of life hidden within the water beneath the surface.