The Earth – The Way We Know It
Earth is the fourth planet from the Sun and therefore the only known astronomical object to harbour living and non-life, in fact supporting life on other planets in our solar system. Less than one percent of Earth’s surface is solid land including oceans and polar regions making it the most uneven planet in the Solar System. The planet has about one hundred and forty-five billion years of age, which is much longer than expected. It also has a thick atmosphere composed mainly of nitrogen and oxygen with water vapor, making up about twenty-five percent.
There are two main classes of planets in our solar system. The first is termed a ‘habitable zone’. This class includes all planets within the star’s system that can support complex life like water, oxygen and temperature (temperature can range from freezing to boiling). The second is a ‘unconfined’ zone which excludes planets with less than the required strength to hold onto a position within the star’s system. If it were not for the planet earth, this portion of the solar system would be dominated by ammonia and carbon dioxide. Today we know that it does include at least one such planet called Earth.
Earth’s orbit around the sun is tidally rotating and therefore it spins on its axis in about ten times for every year of the planet’s orbit. Because of this, the equator is tilted slightly off its axis at all times. As seen from satellites orbiting the earth, the equator appears to be tilted slightly downward at all times although it still rotates through the earth’s orbit at an angle of about thirty degrees from upright.
The solid earth of Earth was formed in a relatively brief period of time about ten million years ago. Geologists believe that dinosaurs were the first animals to inhabit the planet Earth. Over the course of that time, the earth gradually grew into a differentiated planetoid (a rocky body that shares many similarities with the earth) with an atmosphere that contained silica, sulfur and rock dust. The continents were able to spread across the surface of the planet and became differentiated by low pressure and high salt content (soil) as they settled into their respective shapes. When dinosaurs disappeared, they left behind their shells containing rich layers of mineral and salt deposits, which became the basis of what is now the earth’s crust.
About four billion years ago, water began to fill the earth’s atmosphere and the planet began to heat up. Much of the silicate rock dust from when dinosaurs lived turned into fine dust during this time and was held together by organic compounds (such as cellulose) that composed of living cells (which are the basis of life). As Earth began to cool, gravity slowly took control of the planet’s rotation and it spun faster than the cooling ocean. Now the earth spins in a day, not an hour, and is tidally spun on its axis twice a day as it circles the sun.
The earth’s tilt, the tilt of its spin axis and the composition of its atmosphere have remained largely the same for billions of years. Only very recently has mankind set its eye on the moon and perhaps the planets beyond. With the help of technology we may soon be able to detect gases floating around in our solar system and in other alien solar systems. The discovery of “aliens” living on other worlds could prove to be quite exciting. Imagine finding a planet that is similar to earth, only much more molten and much wetter with oceans!