1) Explain how the outward flow of energy from the Earth’s interior drives the process of plate tectonics?
The outermost layer of earth, or lithosphere, is broken up into tectonic plates. The boundaries of the plates and their movement leads to the formation of earthquakes, volcanic activity, creation of mountains, and the formation of oceanic trenches. Tectonic plates are formed from either oceanic crust or continental crust, with many containing both. The movement of the plates varies from 0-100mm in a given year. The movement of these plates comes from the outward energy of flow that comes from earth’s central core. Radioactivity produced from elements within earth’s core, such as uranium, decay and release energy. The plates are able to move because earth’s lithosphere is stronger but has a lower density then parts of the underlying mantle. The heat produced from these processes in earth’s core is transferred to its outermost layers, including the crust and the outer most part of the mantle, through the process of convection. The process of convection creates the horizontal movement that creates the movement of the plates; this horizontal movement tends to go in the direction of the convection currents. At the boundaries of these plates is where they are the weakest; fluid rises and breaks through the crust here causing movement of the other plates.
2) How would you show experimentally that the solar day is longer than the sidereal day?
A sidereal day is method of measuring time in reference to the earth’s rate of rotation. It can also be defined, as the time is takes between crossings of a reference star of any observer’s celestial meridian. Solar day is nearly the same, except instead of a star it is the crossings of the sun. The difference between these two concepts of time explains why we have a leap year every four years.
- 1 solar day: 24 hours
- 1 sidereal day: 23 hours 56 minutes
The difference between a sidereal day and a solar day can be measured experimentally. The aim of the experiment is to determine how long a sidereal day by measuring how long it takes for a bright star to reach another location in the sky, measured on successive nights. The sidereal day is measured in solar hours; and the experiment can be carried out at any point of the year.
- Find a bright star in a well placed location approximately one hour after sunset
- Find a sharp object that can be used as a reference point; this way it is easier to measure the time it takes to reach that location
- The point is to measure how long the star takes to get behind this reference point; this measurement can be done on consecutive nights
- One must be very careful with their time measurement. The observer should set their timepiece to the true solar time, this can be done by checking the time on the internet or by listening to the radio station.
- Each night the start will follow the same path to the reference point but it will take a shorter amount of time each night to reach it. Accurate time measurements need to be taken on each night.
- Earth rotates around its axis once in a single sidereal day, during this time earth moves about 1 degree along its orbit around the sun. This means that after a sidereal day has passed the earth still needs to rotate a bit more before the sun crosses the second meridian.
This difference is reflected in the fact that there is one less solar day then sidereal days. This is why we have a leap year every four years to reflect the 366.26 sidereal days in a single calendar year.
3) Describe the collision-ejection theory of the moon and why we believe it to be the best explanation for the presence of the moon?
The collision ejection theory says that the moon was formed when debris was ejected from earth due to a large object colliding and crashing into earth. Experiments have shown that the energy from such a large collision produced vaporized rock, produced from earth’s crust and mantle but not is core, which is thought to have cooled and formed the moon. This theory explains many facts about the moon, especially its composition and its orbit. For example, the vaporized rock would have lacked volatile or easily evaporated elements such as water. This explains why the moon has a lower water content as compared to earth. The moon also has lower iron content; this is theorized to be due to the fact that these materials sunk into earth’s core before the impact occurred. The ejected material would have come together near the ecliptic plane, causing the moon to orbit much in the same way we know it does today. The impact is also theorized to have tipped earth’s axis, explaining the development of the seasons. Scientists like this theory for the creation of the moon because it explains two separate scenarios; the existence of the moon and the tilt of earth, and therefore makes it a plausible explanation. Indirect evidence to support this theory was found during the Apollo moon landings. Rocks were collected and showed to have similar oxygen isotopes as earth; this happens after turbulent mixing of debris following a massive collision. The composition of the moons’ crust, as well as the finding of KREEP-rich samples, gave rise to the idea that the moon used to be molten; only a large impact could have created such energy to form a magma ocean.
4) How would a planet orbiting a first generation star be different than planets formed today? Could humans exist on that world? Why or why not?
The formation of the first stars fundamentally changed the universe. For example the first stars, altered the dynamics of the cosmos by heating and ionizing the surrounding gases. The first stars also paved the way for the formation of solar systems, by producing and dispersing the first heavy elements. The death of these stars is suspected to have seeded the growth of the massive black holes that are part of galaxies. Planets that orbit first generation stars would have contained hydrogen and helium. Human beings and other living organisms require carbon, oxygen, iron, and silicon one a planet for life to exist. This means that humans could not live on planets orbiting first generation stars. Planets that are formed today, contain the aforementioned elements, hydrogen and helium, but they also contain elements formed during the big bang.
Works Cited
“Lithosphere.” Wikipedia, The Free Encyclopedia. Wikimedia Foundation, Inc. 1 June, 2013. Web. 9 June, 2013
“Sidereal Time.” Wikipedia, The Free Encyclopedia. Wikimedia Foundation, Inc. 26 May, 2013. Web 9 June, 2013
“Giant Impact Hypothesis.” Wikipedia, The Free Encyclopedia. Wikimedia Foundation, Inc. 23 May, 2013. Web 9 June, 2013
Condie, Kent. Plate tectonics and crustal evolution. Burlington: Butteworth – Heinemann. 1997. Web
