Peter Ehry, Torie Kopp, Julia Mudrey, Kim Ratt, Ellise Saunders, Levi Schutz, Chelsea Spilchuk
Formation of the Earth
The formation of Earth began about 4.6 billion years ago from collisions of gas and dust in a massive cloud. Asteroids and small planets eventually formed, and the collisions of these objects led to building the planets in our Solar System. This theory is called the solar nebula hypothesis 1. (Figure 1)
Water has been on Earth since the beginning. Rocks found on Earth that came directly from Earth’s mantle contain small droplets of water composed of the same materials presently on Earth. Detrital zircon crystals formed 4.4 billion years ago have been found to have come in contact with water, meaning that the Earth had oceans at that time 2. This is not to say that water did not come from asteroids and comets; they very well may have added to the Earth’s oceans, but scientists think that water has been on Earth since the time that it formed.
When Earth first formed, the surface was completely molten and there was virtually no atmosphere. When the Earth cooled, an atmosphere composed of hydrogen sulfide, methane and carbon dioxide formed3. Oxygen existed only in water compounds. As the life on Earth progressed, organisms produced oxygen to counteract the methane in the atmosphere. About 2 billion years ago was when oxygen started being produced on Earth4. The oxygen in the atmosphere continued to increase as life on Earth evolved. About 400 million years ago, oxygen made up 20% of the atmosphere.
Life on Earth began about 3.8 billion years ago. At this time, only single-celled bacteria existed. Quite some time later, the life we are familiar with today began to form. Fish first evolved 530 million years ago, followed about land plants and forests in the next 150 million years. Mammals evolved 200 million years ago, and humans did not evolve until 200,000 years ago 5.
This theory proposed that the Moon was really a captured asteroid. This was thought to be true due to the moons of Mars; Phobos and Deimos, for they are captured asteroid moons; which was determined by the non-spherical shape that these moons had. Another hint of a captured moon is if its orbit is in a direction opposite of the planet it orbits 11</sup<. An example of this kind of moon would be that of Neptune’s moon; Triton 12. Because the Earth’s moon is rounded in shape and orbits with the Earth, it disproves the theory that Earth’s moon is part of the capture theory. Also, if you were to imagine the speed of the Moon or asteroid as it whizzed by, it would be improbable to assume that the Earth captured it: the extremely slow approach speed required would imply a far greater likelihood of a collision or ejection 13.
Another reason why the Capture Theory is not a plausible hypothesis for the formation of the moon is because with the age of the Earth being 3.8 billion years old, and the Moon being 4.5 billion years old, it would seem odd for the Moon to be parked for 1 billion years before the Earth was formed and then pull it out when we need it.14.
Giant-Impact Theory was established over a decade ago, and has received more support than many earlier models. Planet formation is thought to start with sticking and frictional coagulation of dust particles in a gaseous nebula that persisted in the circumstellar disk 21. These particles begin to grow in size until there is a gravitational attraction between large-sized bodies. Major collisions between small proto-planets eventually result in objects the size of the Earth 22. It was theorized that the Moon coalesced from a ring of debris produced by such a late-stage collision between two Earth-forming proto-planets 23.
The impact could have splashed enough debris into the Earth orbit to form the Moon. It could also have knocked the Earth into its 23 degree tilt, ensuring the precession of the seasons. A giant impact would have also melted Earth through and through. Some geochemists contended that a giant impact and its inevitable melting of Earth does not jibe with what they know of geochemistry 24. There is hope that the geochemists will likely find some way around this apparent inconsistency.
The Fission Theory was first proposed by George Darwin in 1879. He proposed that the Moon originated from a rapidly spinning Earth on which equatorial gravitative attraction was nearly overcome with centrifugal force 15. The resonant effects of solar tides adding to the centrifugal force to overcome gravity and separate the solar tidal bulge into our present Moon. Once separated, it was driven out to its present position by transfer of rotational energy and momentum through the gravitative effects of the Earth’s tidal bulges 16.
The argument is simple. If you were to put all the mass and angular momentum of the Earth-Moon system back into one single body, the body would rotate in four or five hours 17. In order for it to break-up, it needs to spin much faster. Therefore, in terms of the Fission theory, the angular momentum would have had to be more than three times its present value 18. Don Wise, a professor at the University of Massachusetts and John O’Keefe propose that the only way to get rid of the angular momentum was to suppose that after the fission, the whole system – especially the Moon- lost a lot of mass, because of its lower gravity. Therefore, it would be expected that the immediate result of fission would be two wildly oscillating bodies. These oscillations could be represented by Fourier analysis of the sum of a lot of waves of different periods and different phases 19. Because of different periodicities, it would be a long time before they would be sufficiently close to the proper phase at the proper time, or corotation 20. These oscillations, in the real world, would eventually die out ruling the Fission Theory an unaccepted theory in geochemistry and astronomical formations.