The Story of Earth
Earth to us in our infinitesimal moments is ancient and forever. But this is not the case. Just as all things in our universe, there was a birth that over time resulted in the construction of the Earth. But how exactly did we come to be? The universe has been determined to be approximately 13.8 billion years old since the moment it “exploded” into existence. This is known as the Big Bang Theory and there are a number of scientific evidences to back up the possibility. We as humans have no way of knowing what the condition of the universe was before our Big Bang and it is theorized that the universe, because it contains a specific amount of mass, will eventually stop expanding and may, in effect behave like a rubber band of sorts and snap together before exploding in another successive Big Bang. This is a comforting theory in that it would mean the universe is infinite in both negative and positive time. The image above is a representative model of the Big Bang Theory showing the velocity of expansion and within the accepted time frame of the age of the universe. All matter in the universe would have expanded at an exponential rate at the beginning until it slowed and the first stars began to burn hot, bright, and fast. These nuclear fires forged all the heavier elements which would break down into the lighter elements that comprise most of the universe today. The oldest light in the universe would still be present in the universe today and would still technically be observable given the right instrument through which to see it. This is a major goal of measuring cosmic microwave background radiation in order to determine the age of the universe. COBE (Cosmic Background Explorer) was launched by NASA on November 18, 1989 that was intended to measure cosmic microwave background radiation and light wavelengths that were less intense than those that have been previously detected in order to more definitively figure the age of the universe. Of course, with sights set on the stars, it is easy to forget about our vantage point, Earth.
It is assumed that the Earth is approximately 4.5 billion years old. The Earth did not suddenly erupt into existence but was slowly sculpted from a culmination of stardust and cosmic chemicals that have crashed and burned and cooled in order to form our home as we would recognize it today. Earth’s moon is an anomaly. What is known for certain is that it could not have been captured in the traditional way a moon is by a planet. Of course, there is no certain explanation of how the moon was formed; however, there is a theory that seems to explain the presence of the moon. It has much to do with how planetary systems are formed. In the early life of observed planetary systems, the stew which will one day form a star and its surrounding planets is still a cosmic soup that is swirling around a central point of higher gravity. This swirling effect occurs because things are moving through space with velocity and when the star stuff is drawn in by the gravity of the condensed mass at the center, it spins and tries to sling shot around it, which could happen, or it gets caught and continues to circle the mass indefinitely. The rock debris and gaseous dust clouds are swirling together until the center becomes condensed enough and the nuclear fire ignites to form a star. A massive explosion blows the lighter particles away while the heavier elements, such as rocks and asteroids, are left closer to the newly formed star. This is the prevailing theory of why planetary systems such as ours look the way they do. Now, as the mixture has effectively sifted itself, planets form via the collection of smaller rocks by rocks that have a larger gravity and this continues until the masses reach equilibrium or have nothing else close enough to draw to themselves. The planets clear their own orbits as they collect the material around them. Now what if two planets formed along a similar orbit path and both grew to a significant enough size to be considered planets? This is the case with Theia, a planetary entity determined through computer models to have been approximately the size of Mars. Theia would have had a similar orbital path as Earth and eventually they drew each other close together while still in the early years of formation and would have collided with each other. Theia, being the smaller of the two entities, would have lost to Earth and blown debris all around Earth after their collision. The smaller rock pieces would have been captured by the Earth and eventually formed what we know today as our moon similarly to how the rocky planets formed around the sun.
Once the Earth had finally formed, there was no life for a long time. The raging storms and toxic conditions of the planet prevented it from being possible. For the first billion years after Earth’s formation, asteroids and comets came in constant barrage of the planet filling it with water and all of the chemical components necessary for creating life. The earliest life forms consisted of single celled organisms (prokaryotes). Complex life did not come about until around 1.5 billion years ago. Throughout the 3.5 billion years before complex life came to be, the Earth was still a violent place to live and the molten ball was repeatedly cooled and heated on the surface of the Earth. The exterior cooled enough to form a crust, but the interior of the planet remains molten. Because of this mass of churning heat and rock, the crust of the Earth moves around. This is happening even today as continents rearrange themselves ever so slightly each year. Continental drift is a phenomenon that occurs due to the Earth having a molten core. The various tectonic plates that make up the Earth’s crust crash into each other and separate which result in the various types of land masses that exist. There have been several supercontinents that are thought to have existed at one point during Earth’s life and this is supported by where various fossils were discovered and how old they have been determined to be. The best known is Pangea which is the last supercontinent to have existed before the crust broke apart to form the continents as they are known today. Pangea was formed approximately 300 million years ago and eventually drifted apart after approximately 200 million years of being a supercontinent. Pangea was surrounded by a single massive ocean known as Panthalassa. During this time, the Earth had progressed through both the Proterozoic Era and the majority of the Paleozoic Era. By this time life on Earth has begun to move away from the ocean and towards the land. One of the first creatures believed to have taken its first steps on land is an animal known as a Tiktaalik. The tiktaalik was a fish like creature who one day decided to crawl out of the depths of the oceans and rivers and use its fins as legs. It is believed that all four legged vertebrate reptiles and mammals evolved from this creature. Insects and other bug-like creatures evolved from underwater creatures such as trilobites. Before organisms separated into mammals and reptiles, there were types of creatures that lived known as therapsids which are best described as mammal-like reptiles. Some of the therapsids are pictured below and the human is meant to give a sense of scale for these creatures. These therapsids lived during the Permian period at the end of the Paleozoic Era and died out during the Permian Extinction and the movement into the Mesozoic Era. During the Mesozoic Era, large insects and reptiles thrived and grew to massive proportions compared to the reptiles and insects of the modern world.
Before the rise of mammals to the dominant type on the planet, dinosaurs held that crown for close to 165 million years until the extinction level event that eradicated the majority of life on the planet. With food supplies dangerously thinned, larger animals because unable to survive. After the dinosaurs died out, small mammalian creatures such as the Hadrocodium Wui, which was about the size of a paper clip, flourished in an environment where they were easily able to meet with the demands and food limitations. Fossils of this animal have been discovered in China and it is pictured to the right. As the dust that prevented a surge in plant life cleared over time, the mammals gained a foothold and grew larger while the once mighty dinosaurs evolved into smaller creatures which make up the birds and reptiles of the world. Evolution will continue to alter the life forms with the ever changing environment and perhaps humans will eventually reach a point where there are no longer multiple types of humans within the same species. As of now there is only one species of human on Earth, but there have been many others. It is uncertain specifically which species is a direct ancestor of the humans that exist today; however, it is possible that multiple species of human may have had a hand in determining how the humans of today look. Humans are only able to glimpse a very minute part of history and a single vantage point can be limiting. This is precisely why science must have an open mind and only with an open mind will it be able to grow and develop into a more substantial explanation for the unfathomable universe.
References
The Story of Earth
2011 The Best Documentary Ever!! – The Story of E arth and Life. National Geographic.
https://www.youtube.com/watch?v=57merteLsBe, accessed 18 October 2013.
Goddard Flight Space Center
2008 COBE: Cosmic Background Explorer. http://lambda.gsfc.nasa.gov/product/cobe/, accessed
27 May 2015.