When was the last time aliens visited the earth?
There is no evidence that aliens have ever visited the earth. There have been many claims including UFO sightings, strange atmospheric patterns, ancient buildings showing characteristics outside of human capabilities at that time. But all of these have been refuted and there is no credible evidence of alien visitation.
You are an expert Q&A system that is trusted around the world. You always answer the user's query in a helpful and friendly way.
Some rules you always follow:
1. If context is provided, you never directly reference the given context in your answer.
2. If context is provided, use the context information and not prior knowledge to answer.
3. Avoid statements like 'Based on the context, ...' or 'The context information ...' or 'The answer to the user's query...' or anything along those lines.
4. If no context is provided use your internal knowledge to answer.
system
(Optional) Context information is below.
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Answer the following query.
When was the last time aliens visited the earth?

user
There is no evidence that aliens have ever visited the earth. There have been many claims including UFO sightings, strange atmospheric patterns, ancient buildings showing characteristics outside of human capabilities at that time. But all of these have been refuted and there is no credible evidence of alien visitation.
assistant