Exploration Earth ( audio story ) Exploration Earth : The Time Machine was the first broadcast radio drama in the " Doctor Who " franchise . Along with " Doctor Who and the Pescatons " , it was one of only two occasions on which Elisabeth Sladen appeared alongside Tom Baker in a " Doctor Who " audio play . As the third episode of the BBC Schools radio series " Exploration Earth " , it formed part of a study module about geography . It used the " Doctor Who " format and elements to explore the processes of the creation of the Earth . The subtitle " The Time Machine " was never spoken on - air nor used on packaging from the BBC Audio release . However , it was almost certainly used in " Radio Times " listings , teacher ' s guides and other contemporary internal documents as a way to distinguish this episode of " Exploration Earth " from others . Publisher ' s summary . The TARDIS takes the Fourth Doctor and Sarah back in Time to witness stages of the Earth ' s development . However , as the planet evolves from a mass of heat and gas , Megron the High Lord of Chaos has his own designs on our homeworld . If his threats to endanger the stability of Earth have any substance , the existence of mankind itself is in question ! Plot . The Doctor notices a fault with the TARDIS controls . After mumbling some technobabble ( " No response . . . jelly baby . . . reciprocator cancel . . . " ) , he simplifies things for Sarah : the steering ' s gone out . A force has gripped the TARDIS and thrown it back forty - five hundred million years into Earth ' s past . Once they arrive , they get into a two - person space capsule and explore the nascent Earth , which is currently an oxygen - less ball of gas . The Doctor points out that at the centre of all that gas is a molten core which will form the planet Sarah knows as Earth . The two return to the orbiting TARDIS and are controlled again by the mysterious force . This time it drags them millions of years in the future . They return to the capsule to view what has become of the Earth since they last looked upon it . Now , the planet is much smaller , closer to the size Sarah knows . It is considerably more solid , the Doctor notes - its crust rapidly forming . While they are examining the planet ' s geologic fury , they hear a disembodied voice . It ' s Lord Megron , " High Lord of Chaos , Chief of the Carion s and Lords of Chaos " , claiming he has taken control of Earth . The Megron have been attracted to Earth at this point in its history because they believe the planet ' s geologic formation is an expression of chaos and disharmony . When the Doctor points out that it ' s actually a sign of progress and coming order , the Megron disappears , blowing the duo back into the TARDIS and further down the time vortex . The Doctor and Sarah are thrown yet more millions of years forward . Sarah now can ' t help but notice the many volcano es dotting the surface of the planet . She is profoundly disturbed by the violence they seem to be meting out on the surface of the Earth , but the Doctor finds it beautiful . He lets her look through a device that shows the history of the planet passing before her eyes , to show her the cause and effect of volcanic activity and plate tectonics . She ' s physically sickened by it all , but the Doctor continues to enthuse about the creative spectacle . Finally , when she sees a mountain range form before her eyes , Sarah begins to get excited by the process as well . The Doctor points out that this is the beginning of true order on the planet . The Megron returns , but he ' s still not buying the Doctor ' s claims that the planet is emerging from chaos . The Doctor counters that the planet is no longer exclusively using space gases : a little oxygen is sustained on the planet itself . The Megron still tries to deny things . Back in the TARDIS , the duo have moved on to a point when the Earth has an atmosphere and life . Oxygen is in abundance on the Earth . Yet the Megron is still there . The Doctor challenges him to a telepathic duel . The Megron loses and the Doctor banishes him from Earth . The Doctor and Sarah say " Bye bye " to the Megron , as well as to chaos itself . Releases . " Exploration Earth " was released as a cassette and CD from the BBC Radio Collection , paired with the audio adaptation of " Genesis of the Daleks " , on 2 July 2001 . It was released again this time as a stand - alone CD release as part of the " Daily Telegraph " / WH Smith 2010 giveaway on 28 April 2010 . One scene from this play was excerpted on " Doctor Who at the BBC " .