In this 800,000-year climate record from Antarctica, we see that carbon dioxide concentrations have consistently ranged between parts per million while the climate system oscillated back and forth between glacial and interglacial periods.

80 - 280 ppm

Explanation:

The difference between the glacial and interglacial periods reached about 80 ppm for carbon dioxide and 300 ppb for methane. The cause of this is the oceans and slow geologic process and the accumulation of freshwater in ice sheets.

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference. 

What are the following resources?