Determine how fast the southern ocean is spreading between australia and antarctica: remember that cm-centimeters, km-kilometers, my-millions of years, yr -years remember that a rate (speed) is equal to the distance divided by the time to convert km/my to cm/yr, just divide by 10 step#1: first, measure the distance between australia and antarctica in crn on your large world map (not the piece of paper! ): distance on map in cm step#2: convert the map distance to the real distance by multiplying by the map scale (358km/cm) distance on earth in kilometers (km)- step #3: the age of the oldest crust near australia and antarctica where you measured. this is the age of the oldest ocean floor on the line between the two points. time -age of the oldest crust in millions of years step #4: calculate the rate of opening (rate-distance / time) in both km/my and cm/year. (remember that 1 km/my -10 x cm/yr or 1 cm/yr show your work. 0.1 x km/my)