~~true or false~~
~the outer planets are small, rocky planets with iron cores. --t or f?
~it is unlikely that the sun formed alone. it probably formed with a cluster of stars like the sun. -- t or f?

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