Comic Title: Rip Hunter... Time Master #12
Publisher: DC (National Periodical Publications, Inc.)
Address: 575 Lexington Avenue, New York, NY
Cover Date: Jan/Feb 1963
On Sale Date: November 8, 1962 Newsstand Date November 8, 1962
Source: House Ad, House of Mystery #130, Page 21

Copyright Date November 8, 1962
Source: Library of Congress, Periodicals 1962

Frequency: Bi-monthly
Cover Price: $0.12
Page Count: 32
Editor: George Kashdan

Title: "The 2,200 Year-Old Doom"
Pages: 25

Feature(s):
Rip Hunter (of Earth-1)

Writer: Jack Miller
Artist: John William Ely

Reprinted In:
Showcase Presents:Rip Hunter, Time Master Vol. 1 TPB (2012)

Feature Character(s)

• Rip Hunter (last appearance in Rip Hunter... Time Master #11; next appearance in Rip Hunter... Time Master #13)

Supporting Character(s)

• Jeff Smith (last appearance in Rip Hunter... Time Master #11; next appearance in Rip Hunter... Time Master #13)
• Bonnie Baxter (last appearance in Rip Hunter... Time Master #11; next appearance in Rip Hunter... Time Master #13)
• Corky Baxter (last appearance in Rip Hunter... Time Master #11; next appearance in Rip Hunter... Time Master #13)

Villain(s)

• A tribe of ancient Britons (Caradoc named; no further appearances)
• Several mutated prehistoric animals (no further appearances)

Other Character(s)

• Professor Blake (mistakenly called Professor Blair once in this story; last appearance in Rip Hunter... Time Master #11; no further appearances)
• Various unnamed scientists from the future (no further appearances)

Comments:
Chap. 2: "The Impossible Beasts of One Million B.C."
Chap. 3: "Earth’s Last Chance"

Synopsis:
Rip and his team travel to ancient Briton to destroy a meteorite which threatens to poison the atmosphere of modern day Earth. After failing to destroy the meteorite, Rip journeys to the future to learn the results of the meteorites poison. He finds that the human civilizations have been forced underground, but he learns from them that similar meteorites landed on Earth and were destroyed millions of years in the past.

With the new information, Rip travels to prehistoric Earth and finds several other meteorites which have been rendered inert by some black clay. Rip gathers the clay and returns to the future where he uses it to destroy the poisonous meteorite. The future civilization is then able to return to the surface.