Terraforming Mars begins with altering the physical and chemical composition of Mars to allow other organisms to survive. Increasing the temperature, the availability of liquid water, higher atmospheric nitrogen and oxygen concentrations, and large-scale physical changes are all essential to terraforming Mars. Extremophilic microorganisms that are able to survive Mars's harsh conditions may be a pioneer species on present-day Mars to help change its chemical composition to allow for other microbes to thrive.