Re: What was the largest known explosion to occur on the Earth?

What was the largest known explosion to occur on the Earth?

This is a difficult question to answer, since no one definitely knows 
the energy produced by explosions that happened very long ago.  
Estimates have been made, and here are some possible answers to 
your first question:

The largest explosion event to have occurred on Earth was probably 
due to the impact hypothesized to have occurred approximately 4.6 
billion years ago when a Mars-sized object impacted into the Earth, 
creating the Moon.  This object would have blasted large amounts of 
vaporized rock into orbit around the Earth, which accreted to form the 
Moon. 

The impact that is thought to have caused the extinction of the 
dinosaurs (and many other species) occurred at the Cretaceous-
Tertiary (KT) boundary, approximately 65 million years ago.  The 
impacting object is estimated to have been 6 to 10 kilometers (~3.75 
– 6.25 miles) in diameter if it were a stony asteroid, or somewhat 
larger if it were a comet.  The resulting crater (named Chicxulub) is 
somewhere between 145 – 180 kilometers (91 – 113 miles) in 
diameter and is located on Mexico’s Yucatan Peninsula.  The energy 
given off by this impact is estimated to be 100 million (100,000,000) 
megatons of TNT.  In comparison, the impact that formed Meteor 
Crater in Arizona (crater diameter = 1.2 kilometers (0.75 miles), 
formation age = 50,000 years ago) produced between 15-20 
megatons of TNT.  

There were probably more explosive impacts in Earth’s history, but 
the craters are hard or impossible to find, due to erosion and plate 
tectonics (the oceanic crust of Earth is all younger than 200 million 
years old, and is protected by the water in the ocean, so any craters 
formed before 200 million years ago have been recycled with the 
crust into the mantle, and the ocean probably prevented most 
impacting objects to reach non-shallow parts of the ocean floor).  
Thus it is impossible to say whether or not the KT impact was the 
most explosive impact on Earth after the Moon-forming impact.

The following are a sample of large explosions that have been 
observed by humans:

Krakatoa is a volcano located on an Indonesian island.  In 1883 it 
erupted, producing the most violent volcanic eruption recorded in 
human history.  Its total estimated energy yield was 200 megatons of 
TNT.  

Tunguska – In 1908, the Tunguska fireball was produced over 
Siberia, probably caused by a stony object, about 50 meters across.  
This object did not reach the ground (and thus did not produce a 
crater), however it created a large destructive shock wave in the 
atmosphere, which felled an estimated 60 million trees over 2,150 
square kilometers (840 square miles).  The blast produced energy 
equivalent to 10 – 15 megatons of TNT.

Hiroshima – The bomb dropped on Hiroshima in 1945 can be used 
to compare the energy values produced by natural events to the 
explosions produced by humans.  This atomic bomb produced 
energy equivalent to 15 kilotons of TNT (or 0.015 megatons of TNT).  

The largest nuclear weapon ever produced was the Soviet 
thermonuclear Tsar Bomba ("King of Bombs"), which had an 
estimated yield of 100 megatons of TNT.  A scaled-down 50 megaton 
version of Tsar Bomba was tested in September 1961, in the largest 
man-made explosion to date.  To put this into perspective, if 
detonated, the 100 megaton Tsar Bomba would have produced more 
energy than the impact that produced Meteor Crater and of Tunguska, 
and would have had half of the yield of Krakatoa.

The link below is for a good graph comparing the energy given off by 
the KT impact and that given off by Tunguska.  You can easily plot the 
values for other explosions on this graph as well. http://
gdcinfo.agg.emr.ca/crater/paper/images/nucwin.gif

(the picture is from good cratering website: http://gdcinfo.agg.emr.ca/
crater/paper/index_e.html )


What were the physical effects of the KT impact on the planet?

The following website is an excellent reference about the KT impact.  
The menu bar on the left provides good links explaining the possible 
regional and global effects of the impact, and estimated extents of 
damage.
 http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/
Discovering_crater.html