Depression increases your risk of a number of diseases and other conditions by, for example, increasing levels of stress hormones such as cortisol or adrenaline. Depression can affect the immune system, making it harder for your body to fight infection. Vaccinations are even less effective in people with depression.
The total surface area of the Earth is about 7008510000000000000â 510 million km2 (197 million sq mi). Of this, 70.8%, or 7008361130000000000â 361.13 million km2 (139.43 million sq mi), is below sea level and covered by ocean water.
1 The surface area of Earth is (pi x Diameter) = 197.38 million square miles (where pi = 3.14159265358979). 2  However, the Earth only has 57 million square miles of land (that's 36.48 billion acres; there are 640 acres per square mile). 3  However, there are only 12 million square miles (7.68 billion acres) of arable land.he world population in year 1 A.D. was 250 million people. The world population in year 1492 was 500 million people. The world population in 1804 was 1.0 billion people. The world population in 1922 was 2.0 billion people (doubled in 118 years; increasing on average by about 23,000 per day).