<span>- genetic drift
</span>Which mechanism affected the gene pool of the immigrants that entered the United States through Ellis Island?
NOT:
- gene flow
- gene mutation
<span>- natural selection</span>
Climate change
Greenhouse effect
Some heat energy from the Earth’s surface escapes into space. If too much heat energy escaped, the planet would be very cold. However some gases in the atmosphere can trap escaping heat energy, causing some of it to pass back to the surface.
These are called greenhouse gases, and they keep our planet warm, which is a good thing. Carbon dioxide is an important greenhouse gas.
Increasing carbon dioxide levels
Humans burn fossil fuels such as oil, coal and natural gas. The energy released is used to power cars and other machines, to generate electricity, and to keep buildings warm. The burning fuel releases waste gases, including carbon dioxide. As the human population increases, more fuel is used, and more carbon dioxide is released.
Global warming
The extra carbon dioxide increases the greenhouse effect. More heat is trapped by the atmosphere, causing the planet to become warmer than it would be naturally. The increase in global temperature this causes is called global warming.
Hypoxic waters kill high levels of aquatic species, disrupting the food chain and habitat. In addition to wrecking ecological havoc, the dead zone can be a financial drain on coastal communities.
The chemical substance in adult male pig's urine, which can also be found in other mammals, is called Puberty Accelerating Pheromone. It is also found in boar's saliva, and was said to be responsible in inducing early puberty in young female piglets.
