The Martian rains activate the dormant lichen in the ground. The lichen grows rapidly and ensnares Henderson (Gerald Flood) and Mary Meadows (Pamela Barney). Just when they think all is lost, a cold wind comes up and begins to freeze the lichen. Now that the water the lichen has absorbed is freezing, Henderson is able to break the lichen, freeing himself and Mary.
In the meantime, Harcourt Brown (George Coulouris), with Geoff (Stewart Guidotti) and Margaret (Hester Cameron) in tow, reaches the summit of the ridge. He looks over and sees the lichen but no higher life forms. They turn back North and end up finding Henderson and Mary, who are returning from the polar cap.
The going is treacherous and just before they make it back to the rocket Mary falls into some thick Martian dust that has similar properties to quicksand. Geoff and Brown are sent back to the rocket for some rope. Henderson manages to get Mary out of the quicksand as Geoff rushes back with the rope.
Now, the only one in the rocket, Brown blames everyone else for his not finding any intelligent life on Mars. He tells himself that had he gone further South he’s sure he would have succeeded. He decides to take the MR-4 and abandon everyone else on the surface of Mars.
Lichen is a complex life form. It is a composite organism that arises from algae and fungi living in a symbiotic relationship. There are approximately 3,600 species of lichens in North America alone and about 17,000 species worldwide. They do not have any roots, stems or leaves. They are used to make dyes, perfumes and medicines. They are also a food source for many animals. Most produce asexually in moist conditions. In dry conditions they will crumble and be carried on the wind similar to spores.