Learn : if an asteroid hit the Earth what would really Happen ?

So, what if an asteroid were to hit Earth today? Any asteroid falling from the sky would have a tremendous amount of energy. Here's a typical example. In 2028, the asteroid 1997XF11 will come extremely close to Earth but will miss the planet. If something were to change and it did hit Earth, what you would have is a mile-wide asteroid striking the planet's surface at about 30,000 mph.
An asteroid that big traveling at that speed has the energy roughly equal to a 1 million megaton bomb. It's very likely that an asteroid like this would wipe out most of the life on the planet.

A rendering of an asteroid colliding with Earth.

It's difficult to imagine 1 million megatons, so let's try some smaller sizes. Let's say that an asteroid the size of a house crashed on Earth at 30,000 mph. It would have an amount of energy roughly equal to the bomb that fell on Hiroshima -- perhaps 20 kilotons. An asteroid like this would flatten reinforced concrete buildings up to half a mile from ground zero, and flatten wooden structures perhaps a mile and a half from ground zero. It would, in other words, do extensive damage to any city.
If the asteroid is as big as a 20-story building (200 feet on a side), it has an amount of energy equal to the largest nuclear bombs made today -- on the order of 25 to 50 megatons. An asteroid like this would flatten reinforced concrete buildings five miles from ground zero. It would completely destroy most major cities in the United States.
By the time you get up to a mile-wide asteroid, you are working in the 1 million megaton range. This asteroid has the energy that's 10 million times greater than the bomb that fell on Hiroshima. It's able to flatten everything for 100 to 200 miles out from ground zero. In other words, if a mile-wide asteroid were to directly hit New York City, the force of