This could also be called laws of nature. These are the rules that underlie how the universe works. Such a 'law' would be the law of gravity that states that the force of gravity between two objects depends on the masses of each of the two bodies and the inverse of the distance between them squared. This can also be written G = (constant x Mass1 x Mass2)/distance x distance or G = gM1M2/d2 where g is the constant and is called the gravitational constant.
About time
What is meant by the three types of radioactive decay? And how does radioactive decay produce heat?
--- When an unstable atom nucleus changes, the process is known as radioactive decay. One way this happens by nuclear particles (protons or neutrons) changing from one kind to another. A proton in the nucleus can capture an electron and turn into a nuclear neutron. Or a neutron in the nucleus can lose an electron and change to a proton (beta decay). Another thing that can happen is that a nucleus loses two protons and two neutrons. This is a small particle called an alpha particle (alpha decay). In all cases the change in the number and/or type of nuclear particles produces a different element and in all cases energy is given off which is one of the sources of heat inside Earth.
In radiometric dating, how can a scientist tell if a mineral has leaked daughter product (that is it was not a closed system)? Surely if such a thing occurs the age determined is flawed.
---- You are right. If any of the product (daughter) element leaked out we would get a wrong answer and this is a serious problem for dating minerals. One way to get around this is to use the radioactive decay of uranium for dating. The reason is there are two radioactive uranium isotopes with different half-lives. Both are always present, and they decay at different rates. If there is no leakage of daughter, then measuring daughter and parent atom amounts and calculating age will give the same result for both uranium isotopes. If there is leakage, the answers will be different.
If we use meteorites to date the age of Earth, how do we know that the meteorites formed at the same time as Earth?
----This is a good question. We can only suppose this is true because most meteorites have the same age as each other. In addition the oldest rocks returned from the moon are the same age as meteorites, which tells us that at least one other solar system body is the same age as meteorites.
What are the main differences between the geological periods?
----These periods were originally defined because they have different kinds of fossils. So the main differences are the kinds of fossils they have.
Is there anything humans can do to alter the law of superposition?
This 'law' states than younger features, such as rock layers must form on top of older features. Another example would be that a young crater is superimposed on an older surface. The answer is no, once the features are formed there is nothing humans can do to change this. The evidence may be removed but we cannot somehow make it appear as though the younger 'superimposed' feature formed first.
Questions about Earth temperatures and heat
Why is the core of Earth liquid and hot? ----
It is hot because Earth was heated due to the change to thermal (heat) energy of kinetic energy (energy of motion) of particles that came together to make Earth. As the moving particles hit the growing earth and stopped their energy was transformed to heat. This happened faster than the heat could be radiated away so Earth heated up. The temperature in the outer core of Earth is above the melting point of the metal that makes up the core so it is liquid. However, as depth increases, so does pressure. The more the pressure the more heat it takes to melt a material. Eventually the pressure inside the core is great enough that even though it is hot, the metal is compressed into a solid.
Why is the temperature at the surface of Earth what it is?
--- This is due to the amount of electromagnetic energy that comes from the Sun that warms Earth's surface. Also some of that solar energy is absorbed or 'trapped' by molecules in the atmosphere. These molecules later release that energy generating heat. So the atmosphere is warmed. The combination of these processes and the distribution of heat around Earth by motions of the atmosphere and ocean control the temperature of the planet.
What is a mantle plume? -
This is the name given to a feature that we think is a column of hot rock rising from near the core-mantle boundary toward the surface. A way to think about this is it would resemble the column of hot air that rises above a candle flame. This model has been proposed to explain volcanoes that occur at 'spots' on the earth, away from plate boundaries. The way to get these volcanoes is to have a local source of heat - a hot spot. This might be created by the proposed rising column of hot rock, heated by heat transfer from the core to the overlying mantle.
Questions about plate tectonics
Why is continental crust made of less dense rock than the oceanic crust? Why is it much thicker?
---- The answer is that continents are there because they are made of less dense and thicker crust than lies under the oceans. How did this happen? Over time, starting early in Earth history, temperatures in the outer part of the mantle occasionally got hot enough to cause the rock to melt. Rather than melting totally, however, only some of the minerals in the mantle melted. These low melting minerals have a chemistry that includes mostly lighter elements (for example sodium instead of calcium, lots of silicon and not much iron). When the melt (magma) solidifies the result is a rock of low density that remains 'floating' as the outermost layer of the Earth. As this process is repeated gradually very light materials accumulate as crust. When plates collide these very lightest rocks are not dragged down but are scraped off. This causes the crust to thicken. Thicker crust stands higher than thinner crust and makes continents.
Questions about the atmosphere
Is the greenhouse effect a sign of pollution?
The greenhouse effect is a name given to the natural phenomenon that certain molecules in the atmosphere (especially H2O and CO2) trap incoming solar electromagnetic energy and then release this energy again as heat. Human beings have increased the quantities of the molecules that do this (called greenhouse gas molecules). By burning coal, gasoline, gas, etc. we have put more CO2 into the atmosphere than existed before. In this sense the increase in CO2 may be considered pollution. There are other gases also involved added by humans and some do not exist in nature (such as choloro-fluoro-carbons). Nevertheless the underlying phenomenon would exist whether humans were here or not
Why can't humans manufacture ozone and inject it into the stratosphere to counteract the ozone depletion?
Ozone is a relatively short-lived molecule. We can create it but what is created will not last long enough for us to transport it to the stratosphere. Ozone in the stratosphere is created as the energy of sunlight breaks down the O2 molecules. The single O atoms then combine with O2 to make O3. Interestingly enough, human beings do 'manufacture' ozone. This 'low level' ozone is a component of smog, and it is created as nitrogen-oxygen compounds from burning gasoline mix with the atmosphere. Ozone is hazardous as it can cause lung damage when it is breathed in.
Oceans
Is there a way humans could change ocean currents?
Yes, by changing the composition and thus the temperature of the atmosphere. This would change atmosphere circulation and that in turn would affect ocean currents.