Would life on Earth survive if Sun wasn't there? My teacher told me that there are chances that it would but there would be a lack of gases and chemicals and photosynthesis that occurs with light at certain wavelength.
The answer is No, the Earth would not remain in any recognizable form without the Sun.
There would still be a husk of a dead planet with a small amount of energy coming from the residual heat of the core which might be able to sustain chemosynthetic life in small colonies. However, this is a pretty minor amount of energy compared to what we usually receive from the sun, and without an energy input lifeforms aren't able to sustain their unusually low entropic state (i.e. entropy wins the battle with life).
Some other examples of everyday things which would no longer occur (some already mentioned by @fre0n) are:
- There would be no seasons.
- There would be no weather.
- There would be no daytime.
- There would be no liquid water at the surface.
- The surface temperature would drop to near absolute zero
The Earth is as it currently is and has been since most of the Phanerozoic (542 Ma), the Eon of life, because of some important (not exhaustive) characteristics presented here, being:
- its inclination (causes seasons)
- its mass (gravity)
- its rotation (regulate a temperate climate)
- its revolution trajectory around the sun (latitudinal seasonality)
- its internal thermal regime (from the core) - tectonics, heat
- its distance from the sun (abundant water can easily exist in 3 phases)
- the sun's temperature
without the sun, temperature will be less than minus 230 °C (like on Pluton - let's be optimistic). A lot of essential things will be missing for it to be a dynamic system. It will be a frozen planet.
Microbes and virus should be fine.
Regarding photosynthesis especially.
Put simply, the photosynthesis balanced equation is
6CO2 + 6H2O + Sunlight energy ------> C6H12O6 + 6O2
So let's remove the sun and consider the planet as totally frozen, the photosynthesis equation could hardly be balanced because several terms would not be relevant in the first place, such as the lack of available water, and the absence of light and heat for the process to occur:
6H2O + Sunlight energy ------> doesn't work
Popular science has a good write up on this. In short, everything on the surface is doomed in a year or two. Life in the Oceans would last several hundred thousand years. After that, it's probably just microorganisms living near vents at the bottom of the ocean.
The answers posted thus far have correctly pointed out that natural life would cease to exist without photosynthesis provided by the sun, and natural heat sources from the Earth would only be enough to sustain some very simple lifeforms, and even that is a big maybe. However, there is one other possibility that I have not seen mentioned, which is the influence of man-made technology. Technically life could survive on Earth in an artificial environment if there were (for instance) man-made power generators that warmed areas (probably underground for insulation). Clearly all life would be dependent on technological processes that would fail at some point and the likelihood of having replacement parts and mechanics is slim at best. But, the advancements in automated artificial intelligence could one day take this concept much further. Furthermore, if there were an external source of energy that could be used (e.g. if we had much more skill with space travel), that energy could be transported to Earth and used in some way to allow life to exist in a highly controlled artificial environment.
Since the Earth can't orbit around anything (making it a planet) it would float around (like a comet) waiting for a larger object to pull it into its gravitational field. The larger object would probably be a star (like the sun, but a different one). Life might survive?
Or if left tethered, it might smash into another rogue planet, destroying itself in the process. No life would not survive.
Yes, Here is a very interesting discussion on the Thought Experiment of what would happen to the Earth is the Sun disappeared.
http://youtu.be/rltpH6ck2Kc Miles of ice actually act as an insulator. Chemosynthesis will continue.