Immigrants come to these north america countries because of their high standards of living

Yes and no

Explanation:

There are many factors that motivate someone to leave their country.

There are two types of immigrants... those who do it by choice, others who do it by obligation.

Those doing it by choice who come to North-America is mostly for the quality of life and for different opportunities they might not have in their native country.

There are also those who flee persecution and violence, who cannot stay in their native country.  These immigrants yes, seek a better economical future, but mostly a safer place to live.  For them, the relative security of North-American countries is their main goal.

the precambrian aged rocks could be found in australia. australia is a region that has a lot of ancient civilization history from million years ago. in this region, there are a lot of recognizable fossils buried in its land which is considered a precambrian-aged rocks