The african and south american continents are separating at a rate of about 3 cm per year, according to the ideas of plate tectonics. if they are now 5000 km apart and have moved at a constant speed over this time, how long is it since they were in contact?

166 666 666.7 years

Explanation:

We start the question by making the units uniform. We are told that the continents move at 3 cm/year = 0.03 m/year.

We are also told that the continents are now 5000 km = 5 000 000 m apart

So to calculate the time it took for them to be this far apart

t = distance/speed

t = 5 000 000 m/(0.03 m/year) = 166 666 666.7 years

atomic = no of protons.

mass number-atomic number = neutron number