How big is Earth?
The Earth is a relatively small planet in our solar system. Its diameter is about 7,918 miles (12,742 kilometres) at the equator and 7,900 miles (12,714 kilometres) at the poles. The circumference of the Earth at the equator is about 40,075 kilometres (24,901 miles), and its total surface area is about 510 million square kilometres (196.9 million square miles). The Earth has a mass of about 5.97 x 10^24 kilograms, and its gravity is about 9.8 metres per second squared (32.2 feet per second squared).
If I compressed the earth into a black hole, how big would the event horizon be? How long would it take for it to evaporate from hawking radiation?
If the entire Earth were compressed into a black hole, its event horizon would be approximately 1.7 centimeters (0.67 inches) in radius. This is calculated using the Schwarzschild radius formula, which determines the radius of the event horizon for a given mass:

r = 2GM/c^2

where r is the Schwarzschild radius, G is the gravitational constant, M is the mass, and c is the speed of light.

For the Earth, plugging in its mass of 5.97 x 10^24 kilograms yields a Schwarzschild radius of about 8.87 millimeters (0.35 inches). This is the size of the event horizon that would form if the Earth were compressed into a non-rotating black hole.

However, in reality, the Earth cannot be compressed into a black hole by any known means, since it would require an enormous amount of energy to overcome the repulsive forces between atoms and collapse them to a small enough size. But hypothetically speaking, if this were possible, the black hole would eventually evaporate due to Hawking radiation, a process in which black holes emit particles and lose mass over time. The evaporation time of a black hole is proportional to the cube of its mass, so a black hole with the mass of the Earth would take an incredibly long time to evaporate, on the order of 10^67 years. This is far longer than the current age of the universe, which is estimated to be around 13.8 billion years.