From the text below about the history of peanut butter, where can the first reference be traced from?
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### Instruction:
From the text below about the history of peanut butter, where can the first reference be traced from?

### Input:
The earliest references to peanut butter can be traced to Aztec and Inca civilizations, who ground roasted peanuts into a paste.[clarification needed][2] However, several people can be credited with the invention of modern peanut butter and the processes involved in making it.[according to whom?]

The US National Peanut Board credits three modern inventors with the earliest patents related to the production of modern peanut butter.[3] Marcellus Gilmore Edson of Montreal, Quebec, Canada, obtained the first patent for a method of producing peanut butter from roasted peanuts using heated surfaces in 1884.[4] Edson's cooled product had "a consistency like that of butter, lard, or ointment" according to his patent application which described a process of milling roasted peanuts until the peanuts reached "a fluid or semi-fluid state". He mixed sugar into the paste to harden its consistency.[citation needed]

### Response:

The earliest references to peanut butter can be traced to Aztec and Inca civilizations, who ground roasted peanuts into a paste.[clarification needed][2] However, several people can be credited with the invention of modern peanut butter and the processes involved in making it.[according to whom?]

The US National Peanut Board credits three modern inventors with the earliest patents related to the production of modern peanut butter.[3] Marcellus Gilmore Edson of Montreal, Quebec, Canada, obtained the first patent for a method of producing peanut butter from roasted peanuts using heated surfaces in 1884.[4] Edson's cooled product had "a consistency like that of butter, lard, or ointment" according to his patent application which described a process of milling roasted peanuts until the peanuts reached "a fluid or semi-fluid state". He mixed sugar into the paste to harden its consistency.[citation needed]
The earliest reference to peanut butter can be traced to Aztec and Inca civilizations.