earth or the earth? and another article question.

[jose rocha]

Did we use the article "the" correctly in these sentences?
1 - The most serious problem for the earth is the contamination of water.
2- I think the life in the earth is threatened because of the contamination of the water.

[Mister Micawber]

.
#1 is OK; #2 requires the idiomatic phrase 'life on earth': I think life on earth is threatened because of water contamination.
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