Earth, known as the natural habitat for humanity, is the only planet where life fully exists as discovered till now. About 7.8 billion humans live on earth besides the other creatures contributing about 7 percent of the total population that ever existed here.
Earth is our biggest home where we live, our ancestors lived, and our future generation will proceed to live. But have you ever thought about the life history of this planet?. Do you know how this blue planet was born and how it gets converted into a habitat for humanity? Have you ever thought about the phases of the transformation it has undergone? If not, then this article might help you in finding your answers. So, let’s hear the story of the existence of the earth.
Theories of Evolution of Earth
The Core Accretion Theory/Model
The Core Accretion Theory/Model was the first and widely accepted theory worldwide regarding the planet earth’s and other terrestrial planets’ formation.
4.6 billion years ago, the solar system was composed of a cloud of dust and gas called a Solar Nebula.
The gravity collapsed on earth, causing the materials present on their own began to spin, resulting in the formation of the source of energy that is Sun in the center of Nebula.
- Sun began to rise, causing the existing materials to clump up.
- Small particles bounded by the force of gravity drew together into larger particles, and the solar winds swept away the lighter elements like hydrogen and helium from the closer regions leaving behind a heavy rocky material that later builds up in small terrestrial worlds like Earth.
- The impact of solar winds was less on the lighter elements allowing them to coalesce into big giants, later causing the moon’s formation, other planets, asteroids, and comets.
- The heavy surface of the earth formed due to the colliding and binding of the heavy elements together.
- Sequentially with time, the lighter materials created the crust. In contrast, the dense materials sank to the center, and the planet’s magnetic field probably formed, causing gravity to capture few gases. Thus, resulting in the formation of the planet’s initial atmosphere.
- This habitat for humanity suffered an impact due to the presence of large bodies, which caused the capitulation of young pieces of the young planet’s mantle into space. Due to the actions of gravity, small pieces drew together and formed the moon. Click here to know more about the foundation story of the moon.
- The flow of mantle beneath the surface of the crust caused plate tectonics and the movement of large plates of rocks on the surface of the Earth.
- Arising friction and collision gave rise to the mountains and volcanos, which spew gases into the atmosphere.
- The existence of water on earth was due to collisions from the icy bodies of asteroids and comets, which caused the deposition of water on the earth’s surface.
The Disk Instability Model
The core accretion theory gained huge success for the evolution of terrestrial planets. But one point of the theory which states that the gas giants evolved rapidly for grabbing hold of the significant mass lighter gasses was what stimulators were not able to account for as that was a rapid formation process. This widely accepted theory of habit for humanity’s evolution soon faced the migration issue as in the short time the baby planets are likely to spiral into the sun.
Now during these assumptions, a new theory came forward, which was named the disk instability model.
According to this model, ‘ the clumps of dust and gas bounded together in the early stages of the solar system. It resulted in a giant planet as these clumps bounded together gradually with time. The planets developed from their core accretion revivals and trapped the gases, which were lighter and rapidly vanishing. Also, they reach an orbit stabilizing mass, keeping them from marching into the sun and vanishing their existence.’
The theory got evidence when 4 giant planets orbiting at a significant distance around a star HD99799 was observed. Paul Wilson, an exoplanetary astronomer, suggested that many worlds would exist at large orders according to disk instability if dominated. Also, the discovery of Fomalhaut b, an exponent, added more value to the theory.
Pebble Accretion theory
According to the Pebble Accretion Theory, ‘an object during its growth will continue to accumulate pebbled-sized objects generally few inches in diameter rather than sticking to same-sized objects and resulting in the form of a planet. As the object continues to grow in size with thousand years timescale, it would be attracting more pebbles to its orbit by aerodynamic drags resulting in them fusing with them.’
This theory for habitat for humanity and other planets’ life history was proposed by Michiel Lambrechts and Anders Johnson from Lund University in 2012. With his team in his research model, Levison explained how the tiny pebbles resulted in the formation of planets and galaxies seen today. According to Harold Levison’s statement, an astronomer in Colorado to space.com, this model is the first model to be known, which explains the simple structure of the solar nebula to the formation of a giant planet system.
History of the Formation of the Habitat for Humanity
There have been various theories and models formulated for the earth’s formation. However, intensive research of scientists worldwide and major contributions of branches of natural science has made it possible to understand the events of the earth’s past, which are characterized by constant geological change and biological evolution. Geological Time Scale developed describes the large periods of earth’s formation process to the events in its evolution from fireball to habitat for humanity.
Now, the earth’s history has been divided into 4 eons, which are further divided into eras, with periods and epochs being divisions and subdivisions of a particular era. The four major eons are:
- Hadean Eon
- Archean Eon
- Proterozoic Eon
- Phanerozoic Eon
This eon describes the structural changes in the habitat for humanity between 4,540 – 4000 million years ago. Major events that took place in this eon are as follows-
- The earth’s formation from the debris around the solar protoplanetary disk is considered an accretion disk for the stars called T Tauri star and Herbig Ae/Be star. These stars are the young, newly formed stars. The protoplanetary disk is generally a rotating circumstellar disk that is composed of dense gases and dust surrounding the mentioned young newly formed stars.
- There was no existence of life.
- It is inferred that in this phase of the habitat for humanity, the intense meteorite impacts called the Late Heavy Bombardment began around 4.1 Ga and concluded around the end of this eon that is around 3.8 Ga. the Late Heavy Bombardment is a hypothesized event that is predicted to be the collision events that occurred on early terrestrial planets of the inner side of the solar system from large asteroids. The intense impacts of meteorites were predicted due to carter counts on other celestial bodies. Carter counts the method of estimating the age of the planet’s surface.
- The temperature was generally hot in this eon, with volcanoes occurring frequently and an environment like hell existed with earth resembling a fireball.
- Nebular atmosphere existed
- Early oceans of bodies and liquid water possibly existed.
- The formation of the moon took place due to a protoplanet’s collision into Earth.
- A Protoplanet’s Collision into Earth. It is a theory that states that the moon’s formation is due to the ejecta of collisions between a Mars-sized planetesimal with the proto earth in this eon for about 4.5 billion years ago. This theory is also known as the giant impact hypothesis.
This eon has faced the changes in the history of the habitat for humanity between 4,000–2,500. The remarkable events that took place in this eon are –
- At the beginning of this, the earth’s atmosphere was cooled up, but the present form of life could not have survived on that phase of humanity’s habitat due to the lack of ozone layer to block the ultraviolet rays of the sun.
- The prokaryotic life, which is the first form of life, started blossoming up in this phase.
- The prokaryotic life started existing by the process called abiogenesis. Abiogenesis is the natural process from which life started existing from non-living matters such as organic compounds. It is also known as the origin of life.
- The continents of Ur, Vaalbara, and Kenorland are predicted to have started existing in this eon.
- The atmosphere was generally composed of volcanic and greenhouse gases.
This eon displays the time phase between 2,500 – 541 million years ago. The name of this eon translates as early life. The main events that took place in this eon are:
- The cratons grew into continents and modern sizes. Craton is an old and stable part of the continental lithosphere consisting of the habitat for humanity’s topmost layers: crust and the mantle.
- The earliest cells absorbed their energy and food by utilizing the process of fermentation.
- The third atmosphere of the earth started to shape up due to the oxygen produced by bacteria.
- The development of an oxygen-rich atmosphere was the major development that took place in this eon.
- The evolution of photosynthesis made it possible for the living cells to derive energy from the sun.
- Eukaryotes raised gradually in this eon. They became the most complex form of life in this phase of the history of humanity’s habitat, including some form of multicellular organisms.
- An early form of plants and later animals, possibly the early forms of fungi, started forming in this phase.
- This eon has undergone the Snowball Earth Period in its early as well as later phases. The snowball earth was the time in which the habitat for humanity suffered the harsh below zero temperatures.
- The earlier continents of Columbia, Rodinia, and Pannotia may have existed in the same order.
This is the last eon, representing the period between 541 million years ago to present form of the habitat for humanity. The name of this eon translates as visible life. This eon consists of three eras, which are further divided into several periods. The three eras of phanerozoic eon are as follows:
- Paleozoic Era ( 542 – 251 Million Years Ago)
- Mesozoic Era(251 – 66 Million Years Ag0
- Cenozoic era ( 66 Million Years Ago – Present)
The main eventual changes that occurred in this eon includes:
- The complex forms of life that are vertebrates started to dominate the habitat for humanity. These dominated the existing oceans by the process known as the Cambrian Explosion.
- The Pangaea was formed in this phase, which later got dissolved into Laurasia and Gondwana, which further dissolved and converted into the current continents of our habitat for humanity.
- With time life forms expanded and evolved towards landforms, and the fungi, plants, and animals started to appear in their current familiar forms. The familiar forms include annelids, insects, and reptiles.
- This phase of the habitat for humanity has undergone several mass extinctions due to many unfavorable reasons.
- Birds, the decedent of non-avian dinosaurs, and the recent mammals started emerging in humanity’s habitat.
- At the most recent phase of this eon, the modern animal forms, including humans, evolved.
Hence, the planet earth has gone through various developmental and structural changes to get transformed into its present form of habitat for humanity. The transformational story of it is quite fascinating to find out; however, there are unlimited mysteries and solutions of this planet that are yet to be unfolded in the upcoming future