Wenley Moor Affair

The Wenley Moor Affair, as the Seventh Doctor referred to it, (COMIC: Final Genesis) was the first contact between humanity and Silurians in the late 20th century.

Based on conflicting accounts and inconsistencies, the affair occurred in sometime in the 1970s, (PROSE: Transit) specifically 1973, (PROSE: Blood Heat) or the 1980s.

Background
The Third Doctor tried to mediate between the United Nations Intelligence Taskforce and the Silurians, but failed. After combating a virus released by the Silurians and preventing them from altering the Van Allen Belt, Brigadier Alistair Gordon Lethbridge-Stewart bombed the Silurians hibernating at Wenley Moor. (TV: Doctor Who and the Silurians)

Aftermath
Weeks afterwards, the Doctor and Brigadier still weren't on good terms from the event. (AUDIO: Shadow of a Doubt)

The Doctor would again try to make peace when awakened a colony of Sea Devils from hibernation. (TV: The Sea Devils)

Vastra, a lone Silurian who lived in London, was aware that UNIT "once murdered a whole colony of [her] people, as they lay sleeping and defenseless." (AUDIO: Rescue)

Parallel Universes
"The Wenley Moor Affair was a crucial nexus-point in Earth's time stream. A countless number of futures could be claimed from that moment... The divergent realities were near-endless."

- The Doctor

In a sub-universe created by the Monk and Artemis the Chronovore, the Third Doctor was killed with no regeneration, and twenty years later in 1993 humanity was still fighting with Silurians and Sea Devils. The Seventh Doctor would end up destroying this universe, as leaving it to exist would shorten the lifespan of the real universe. (PROSE: Blood Heat)

The Seventh Doctor would later encounter another parallel universe where his third self succeeded in brokering peace, only for it to be threatened twenty years later by Mortakk. (COMIC: Final Genesis)