As a linguist aboard a terraforming mission, you arrive at a new planet. The planet, orbiting a G2V star, has copious amounts of wildlife and some sentient lifeforms. However, you, interpreting an old radio broadcast, hear about some deadly diseases on the planet that may kill alien species, and had killed a superior invading race centuries ago.
Deciding that, while policy dictates that the genocide of sentient species is not allowed, none of your crew want to die from a deadly disease from this planet the natives call "Earth", you decide to fence in a continent (named "Australia") as a nature preserve for the sentients while sterilizing the rest of the planet for your own use. What is the most realistic, cost-effective way for you to do this (fence in the natives and their wildlife)?
A solution would have the following:
- A physical quarantine, which contains all alien living organisms within the "wall". This should block exit of any infectious disease, including bacteria and viruses, as well as anything that may carry the disease.
- Scalability, such that thousands of kilometers may be built with the least expense.
- Failsafes, in case the quarantine gives way.
There is little futuristic tech that you can use here: teleportation portals exist, but are prohibitively expensive, and you need to try to accomplish this with present-ish (22nd century) materials.
EDIT: The natives are bipedal creatures, and seem to have regressed from a society on-par with the aliens to a medieval society.
EDIT 2: The Proxima Conventions on Interstellar Travel and Terraforming state:
No sentient species shall be attacked during the act of terraforming a planet, unless they pose resistance. However, the killing of resistors on the planet is legal under interstellar law. The indiscriminate murder of sentient species due to some resistance is legal under no circumstances.
Resistance is never defined in the treaty, so you can pretty much kill some but not all of the species.
EDIT 3: @Alexander, birds can carry deadly diseases. Alien species may be taken out of quarantine on a case by case basis, but in general all species are quarantined.
@chasly the area can be expanded or contracted as necessary. Australia was used to give an approximation of the size of the zone quarantined. If worst comes to worst, extermination of non-sentients is permitted but discouraged by the Proxima Conventions.