ផែនដី៖ ភាពខុសគ្នារវាងកំណែនានា

{{seealso|Historical geology|Age of the Earth|Giant impact hypothesis}}

 

 

[[Condensation|Condensing]] [[water vapour]], [[comet]]s and [[asteroid]]s hitting the Earth made the [[ocean]]s. Within a billion years (that is at about 3.8 billion years ago) the first [[life]] [[evolution|evolved]], in the [[Archaean]] [[era]].<ref>{{citeweb|url=http://www.spaceref.com/news/viewnews.html?id=258|title=Earth life appeared on land 1.5 billion years earlier than previously thought|accessdate=2009-07-03|publisher=SpaceRef.com}}</ref> Some [[bacteria]] developed [[photosynthesis]], which lets plants make [[food]] from the [[Sun]]'s [[light]] and [[water]]. This released a lot of [[oxygen]] into the [[atmosphere]] or air, making the Earth's surface [[wikt:suitable|suitable]] for life. This oxygen also formed the [[ozone]] [[wikt:layer|layer]] which protects the Earth from bad [[ultraviolet]] [[radiation]] from the [[Sun]]. This protection made it possible for things to move from the deep ocean to the surface. Long ago almost all land was in one place. This is called a [[continent|supercontinent]]. The earliest known supercontinent was called ''Rodina''. Scientists think that soon after this there was a time (the [[Cryogenian]]) when the Earth was almost entirely covered by thick ice sheets ([[glacier]]s).<ref name=snearth>{{citeweb|url=http://www.eps.harvard.edu/people/faculty/hoffman/snowball_paper.html|title=The Snowball Earth|accessdate=2009-07-28|publisher=Harvard University|work=Paul F. Hoffman and Daniel P. Schrag}}</ref> This is called the [[Snowball Earth]] [[theory]].<ref name=snearth />