Afossil of a burrow left by an organism would be an example of what type of fossil?

The oldest rocks in the south atlantic ocean, immediately adjacent to the african and south american continental shelves, are 120,000,000 years old (time). calculate the average rate of seafloorspreading for the south atlantic ocean over its entire existence (hint: use formula: velocity = distance/time): /yr (velocity). now convert that to: cm/yr: