Editing 2925: Earth Formation Site

[[Cueball]] reads an historical marker celebrating the formation of the {{w|Earth}}. As with most historical markers, it claims to rest on the exact spot of the event, that the Earth formed in this specific location. It also specifies the Earth's formation to the precise year 4.45 billion ({{w|Long and short scales|4,450 million}}) BCE.

The absurdity of the sign is threefold:

# The Earth did not form on its surface

# The precise year of the Earth's formation is not knowable

# Historical markers typically refer to events within the past several centuries

'''#1: The Earth did not form on its surface'''

First, the Earth formed at its center, not anywhere on its surface, so an “Earth formed here” sign on the surface is amusingly incorrect.

One may argue that technically the sign is ''above'' the right spot, just as every location on Earth is above the right spot. However, the sign refers to “this location,” not to a spot underground.

If an omniscient observer wanted to mark the spot in space where the Earth started forming, they would need an historical marker floating in space, not on the surface of the (moving) Earth. That’s due to the {{w|Sun#Motion|Sun's 225-million year long orbit around the center of the}} {{w|Milky Way galaxy}} and the movement of the galaxy itself through space relative to other objects.

'''#2: The precise year of the Earth's formation is not knowable'''

Secondly, specifying a single year of formation BCE (Before the Common Era) is an amusingly precise choice. It takes [https://science.nasa.gov/exoplanets/how-do-planets-form/ tens or hundreds of millions of years] for a planet to form. Picking a year would require some specific definition of when a gradually-coalescing mass of proto-planet dust and gas could be considered a planet, as well as the impossible ability to determine when that mass met the definition.

If the precise year was knowable, the probability of the number actually ending in seven consecutive zeros would be on the order of one-in-ten-million.

The topic of what precisely makes a planet — related to the 2006 redefinition of a planet and the subsequent reclassification of Pluto from the solar system's ninth planet to a dwarf planet — has been covered before in [[473: Still Raw]] and referenced in other XKCD comics.

There is some poetry in the idea that there was a precise year, some 4.45 billion years ago, that was the first true year, the first Earth orbit around the sun. By definition, the Earth is the same age as the number of Earth orbits that have ever taken place.

 

'''#3: Historical markers typically refer to events within the past several centuries'''

 

 

'''The title text'''

Also, a historical marker referring to the Earth’s core could be placed anywhere on the surface, and its specific location in the real world wouldn’t mean anything; just as before, every spot on Earth is above the right spot.

* {{w|File:Prime meridian.jpg|Prime Meridian longitude}}

'''Analysis'''

The comic and its title text are actually inverse jokes of each other: The historical marker in the comic assigns an attribute of the Earth’s '''center''' (the site of formation) to a spot on its '''surface''', while the historical marker mentioned in the title text assigns an attribute of '''surface''' locations (latitude and longitude) to the Earth’s '''center'''.