If a needle hit the Earth at the speed of light, it would release an enormous amount of energy. The kinetic energy of an object is proportional to its mass and velocity squared. So, if a needle were to travel at the speed of light, its kinetic energy would be infinite.
In reality, no object with mass can travel at the speed of light. However, it is a fun thought experiment to consider what would happen if something like this did occur.
The impact of a needle traveling at the speed of light would be devastating. It would create a massive explosion, releasing energy equivalent to millions of tons of TNT. The impact would also create a shockwave that would travel through the Earth, causing widespread damage.
The exact effects of the impact would depend on where the needle hit the Earth. If it hit a populated area, it would likely cause widespread death and destruction. If it hit the ocean, it could create a tsunami that would devastate coastal areas.
Even if the needle hit an uninhabited area, the impact would still be significant. It would create a crater several miles wide and several miles deep. The impact would also release large amounts of dust and debris into the atmosphere, which could cause global climate change.
In short, if a needle hit the Earth at the speed of light, it would be a disaster of unimaginable proportions.