ProfessorStephenHawkingthinksthehumanspecieswillhavetopopulateanewplanetwithin100yearsifitistosurvive.Withclimatechange,pollution,deforestation,pandemicsandpopulationgrowth,ourownplanetisbecomingincreasinglyprecarious.PlanetEarthhasbeenhometohumankindforover200,000years,butwithapopulationof7.5billio...