1) Explain how the outward flow of energy from the Earth’s interior drives the process of plate tectonics?
The earth’s composition consists of a crust, mantle and core. The earth’s core consists of elements like uranium which are radioactive. Due to the phenomenon of radioactivity, these elements decay and trigger a reaction. Because of this a large amount of energy is produced in the core and inner core of the earth. Because of this energy, the core of the earth is very hot and in a molten state. This heat is transferred from the core to the crust by the process convection currents formed in the molten core, creating a cycle of rising and falling of the molten material. This causes horizontal movements of the earth’s continental plates below the crust layer. At places where the crust has fissures or the layer is weak enough of break open, the molten material oozes out pushing the adjoining plates. This makes the plates to slide over it in the direction of the convection currents, creating new surfaces and changing the topography of the area. This is how the outward flow of energy from the earth's interior drives the process of plate tectonics.
2) How would you show experimentally that the solar day is longer than the sidereal day?
Usually in our day to day life we use the solar day as a measure of time. It is basically the time period between the two successive crossings of the sun from the point of observation on earth. This time period is 24 hours. Sidereal day is basically a star day. It is measured by the crossing of reference star at the observer’s celestial meridian. This time period is 23 hours and 56 minutes.
This difference between the solar day and the sidereal day can be demonstrated by an observational experiment with the aim to determine the length of the sidereal day in solar hours. This shall be done by measuring the time a bright star takes to reach the observation point on different nights. Following are the steps to be followed to conduct the experiment –
- On the first day of the experiment measure the exact time at which selected star disappears behind the sharp reference object. Repeat the observation daily for several days.
- Before starting the experiment, one must be sure about the calibration of the clock that shall be used to record the time observation each day. It should be in perfect sync with the solar time. This can be easily done by tuning the clock with the radio or national news timings.
- Each night the star would travel the exact same path to reach the reference point, but as compared to the solar day timing we shall notice some difference in the time at which it reaches the same point. This time should be measured accurately for the days to follow.
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 can be understood by its literal meaning i.e. ejecting out of a part due to the collision of two objects. This theory lies in line with the age-old fact of the formation of moons in the solar system. This theory states that at some point of time in the past earth was struck by a planetesimal of the size of mars at such an angle, that the collision, lead to the disintegration of some material from the earth’s surface which got placed into the orbit around earth. This material was a part of the earth’s crust and mantle. It did not contain the core’s iron-rich mass.
This theory justifies the known facts about the moon, like, the impact would vaporize the rock and it would lose all its volatile elements and water contained in it, leaving the moon low in water, which we now know as a fact. Also, moon contains very less iron rich matter, which can be explained by the fact that during the collision only a part of the lighter rocks of crust and mantle splashed out and the iron rich heavy minerals remained in the core of the earth. This impact also seems to have tilted the earth’s axis bringing in the variation of seasons. Also, the debris of the collision would orbit near the elliptical, if the impacting planetesimal’s orbit had been near to it. This theory verifies the existence of the moon as well as the tilt of the earth’s axis and thus is widely supported by the scientists.
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 First generation stars and the planets orbiting them consisted only of the elements formed in the big bang. These were mainly helium and hydrogen. With the passage of time and the chain reactions that happen in a star, other heavier elements have been formed. Thus the planets formed today are made up of these elements as well as those from the big bang. For life to exist on any planet carbon and oxygen are the basic elements required. Also, elements like iron and silicon are crucial for the structural composition of the planet that can support life. Therefore, as the earlier planets consisted of only hydrogen and helium, human life could not have been present on them.
Sources
User’s Guide to Night Sky - Solar Days and Sidereal Days. Department of Physics. Durham University.
http://www.dur.ac.uk/john.lucey/users/e2_solsid.html
Martha Haynes. History of Universe. Astronomy 2201.
http://www.astro.cornell.edu/academics/courses/astro201/astro201.html
Larson. B. Richard, and Bromm Volker. The First Stars in the Universe. Scientific American. 2004.
http://www.astro.yale.edu/larson/papers/SciAm04.pdf
Windows To The Universe. National Earth Science Teachers Association.
http://www.windows2universe.org/earth/moon/collision_ejection_theory.html
How Plates Move. Plate Tectonics.
http://www.platetectonics.com/book/page_4.asp
