Updated: December 11, 2018
BEHIND THE SCENES (GIANT CYCLOPS)
There Were Giants in the Earth Season One (Original Air-Date October 6, 1965)
Sneaking out of the Jupiter-2 at night against his father's orders, Will goes to repair the chariot. While he is working, the Robot follows him in order to carry out Dr. Smith's orders to eliminate non-essential personnel as opportunity arises. Will manages to radio for help and to keep the Robot occupied with a testing program until help arrives and the Robot is deactivated.
The next day, John announces his plan for the crew to turn their campsite into a long-term, self-sufficient community. Despite the native soil's unknown characteristics, Smith plants peas in the ground. These quickly grow to monstrous proportions, full of dangerous, worm-like creatures and must be destroyed. John later examines the remains of the plants and the soil and determines that a microscopic life form pervades both, and may be responsible for all lifeforms on the planet having the potential of great size, and great danger to the Robinsons in consequence.
When the local vegetation begins dying off, apparently due to frost, the Robinsons investigate. After a visit to their weather station, they are able to determine that the weather will only continue to grow colder, dropping to as much as 125° below zero. While John and Don are at the station, they are menaced by a gigantic cyclops and driven into a small cave to escape it. Will spies the creature with the Jupiter 2's radio telescope and races to the weather station, where he is able to kill the monster and save his father and Don.
Because of the dropping temperatures, the Robinsons plan to abandon their campsite and head south to warmer temperatures. When the chariot has been loaded in preparation for their journey, Penny is nowhere to be found. With only a short time before departure will be futile, John takes the jetpack to search for her. When he finally locates her and returns her and the bloop to the Jupiter-2, the chariot must leave immediately.
As they begin their journey, Dr. Smith and the Robot remaining behind, they encounter another gigantic cyclops which throws boulders at them, but Don is able to bring it down with a laxer blast. Their journey must be interrupted in order to make repairs to the chariot, damaged by the cyclops' attack and the Robinsons pitch camp for the night. They are able to resume their journey the next day, but soon encounter a ferocious electrical storm and they are forced to seek shelter in a nearby cave. Finding the ruins of an ancient civilization there, the children, Don, and Judy become trapped in a small chamber. John and Maureen race to free them as the ruins begin to crumble when powerful tremors rock the planet.
"Data inaccurate... data inaccurate... humanoid not 18 meters tall" - the Robot
The most interesting alien creatures in this episode were the cyclopian giants, resembling those in Greek mythology. Could a humanoid actually be 18 meters tall? Eighteen meters is roughly ten times normal human height. If a human being were scaled up ten-fold in size, its bones would be ten times as thick as those of a normal sized human. However, volume does not scale linearly with size. A ten-times bigger human would have one thousand times the volume of a normal human. One thousand times the volume would mean one thousand times the weight. The giant's bones would be far to thin and fragile to support this much weight. Thus, assuming flesh and bone like ours, 18 meter tall giants are not possible.