Answer;
The Huronian Supergroup is particularly exciting and interesting because, by chance, these rocks were laid down at a period when the atmosphere underwent a transition from containing no free oxygen to containing at least some free oxygen.”
Explanation;
The Huronian
Supergroup, a massive
formation of rock laid down
gradually between about
2.5 billion and 2.2 billion
years ago, precisely the
period when oxygen
began to accumulate in the
atmosphere. The Huronian Supergroup is 10 or 11
kilometers (six or seven
miles) thick and extends well below ground
