Answer:
b. flat rotation curves in spiral galaxies
Explanation:
Dark matter accounts for majority of the matter in the universe (about 85%). It is considered to be composed of subatomic particles which are yet to be discovered. Dark matter cannot be observed because it does not emit light that can be detected. Only its gravitational effect is visible.
Astronomers when calculated the mass of the visible matter and tried to account for the observed speed of stars in the galaxy, there was a mismatch. To understand what caused this mismatch, astronomers gave name to the invisible matter as the Dark Matter.
The expected velocity of stars should decrease away from the near the center of the galaxy but a constant velocity of stars was observed that is a relatively flat rotation curve was obtained.
Thus, flat rotation curves in spiral galaxies in an evidence of Dark Matter.
The ozone layer protects us from the harmful emission of rays directly to the environment. Absent this added layer of protection we humans will be susceptible to various forms of cancer due to over radiation and eye problems such as cataracts. It is estimated that 10% of the world's population will face the consequences of ozone depletion this year and these numbers were continue to rise as time progresses.
Religion, because it's something that families and cultures would pass down through their generations
