If I create default empty based on no archetype Maven project in Eclipse, it will be based on J2SE-1.5.
Maven
Eclipse
J2SE-1.5
It's consistent with source and target settings of maven-compiler-plugin, which are 1.5 by default.
source
target
1.5
If you change them, generated project will use different version of as well:
org.apache.maven.plugins maven-compiler-plugin 3.1 1.7 1.7
Note that if you change compliance settings of Eclipse project without changing of maven-compiler-plugin settings, your Maven builds would be inconsistent with your Eclipse environment.
maven-compiler-plugin