, and drastic changes in oceanic chemistry. Mountains and continental drift helped shape the planet’s land masses into a formation not unlike present day. Plants were the first multicelled organisms on Earth. At about 600 million years ago, the first appearance of larger metazoans occurred after a sudden increase in atmospheric oxygen. The element oxygen is a key to the appearance of larger animals due to their metabolism system requiring the gas for survival. Could this exact process or a similar one have happened to create life on some other world in the universe? To answer this, we must determine the guidelines for what makes a planet suitable for the appearance and evolution of Earth-like life. It has been hypothesized that for a world to be capable of inducing and sustaining life it must be located within a certain habitable zone or HZ. A habitable zone is defined as a region where heating from the central star provides a planetary surface temperature at which water can exist as a liquid. This distance range varies for each star-planet system as it depends on the magnitude of a star’s brightness. A larger and brighter star than the sun would have a HZ farther away and a smaller star would have a HZ closer to it. But there is a paradox here, if a planet forms close enough to a star to be in its habitable zone, it typically ends up with little water and hardly any carbon compared to bodies that form outside the HZ. Compared to other stars, our sun is not typical. Over 95% of all stars in the universe are less massive than the sun. For multiple star systems, the habitable zone gets more complicated. Two-thirds of solar type stars (M class) in our Milky Way galaxy are members of binary or multiple star systems. When two stars are orbiting close together, their planets orbit both stars. When the stars are far apart, their planets only orbit one of them. Some problems with this situation include: Planets may not be able to f...
