Why was an asteroid with only a 10-15 km (7-8 mile) width able to wipe out the dinosaurs and cause the extinction of 75% of all species on Earth?

Question

That width is less than the distance I drive from my house to the grocery store. Why was that size of an asteroid able to cause such catastrophic damage?

In: 21

Answer 1

The escape velocity of earth is 11km/s which is the lowest speed an object can hit earth if you ignore the atmospheric drag, On average the speed is 18km/s but it can be as high as 30km/s

The kinetic energy is E=m v^2 /2 where m is the mass in kg and c v the speed in m/s. TNT release released 4.6 million joules when it detonate. so if we solve 4.6 *10^6 =v ^2 /2 we get the speed when kinetic energy is equal to the explosive energy of the same amount of TNT. The answer is v=30m/s = 3km/s.

so the slowest impact is 11/3 = 3.6 time faster and the kinetic energy is 3.6^2 = 13 times larger. So the slower possible meteorite has the same energy as 13 it’s mass in TNT

What is the mass of a 10-15km asteroid? Let’s use a sphere with a 5km =5000 m radius. The volume is 4/3 pi r^3 so the volume is 5.2 * 10^11 cubic meter. Rock has a density of around 3 tonnes/m2 so the mass is around 1.5 * 10^12 tonnes. Multiple by 13 and we get the energy in tonnes of TNT 19.5 * 10^12 tonnes of TNT

Nuclear bomb yields are in tones of TNT and 1 megaton =1 million tonne = 1 * 10^6. This means the energy in the meteorite is more than 19.5 * 10^12 / 1 * 10^6 = 19.5 * 10^6 = 19.5 million atomic bomb with a 1 megaton yield. 1 megaton is a large strategic nuclear weapon that can destroy a city. The total energy in all nuclear weapons on is equal to around 3 000 1 megatons of bombs so we talk about 6500x more energy realized at once in one location This is a minimum energy calculation

I you look at the number from Wikiepada the estimated impact speed is 20km/s and 100 million 1 megatonne nukes.

It is the global fire storms and all the particles that then will be on the atmosphere and result in global winter a couple of years long when practically no sunlight reaches the ground that killed the dinosaurs and most other life on earth. Technically all dinosaurs did not die, birds are dinosaurs and their ancestors did survive.