Which of these is a characteristic of index fossils? 1. Found in the topmost rock layer
2. Found in many layers of the same rock
3. Have already established relative age
4. Are limited to a particular geographic location

Why is the huronian supergroup rock formation particularly interesting to scientists? because it looks like a cross-section of a giant, stone encyclopedia because it formed during the period when oxygen began to accumulate in the atmosphere because it contains unusually large amounts of oxygen and sulfur because it dramatically altered the planet's development when it first formed