Many of the technologies on which blockchain is based were in the works long before bitcoin appeared.
One of these technologies is the Merkle tree, named after computer scientist Ralph Merkle.
Merkle described an approach to public key distribution and digital signatures called "tree authentication" in his 1979 Ph.D. thesis for Stanford University.
He eventually patented this idea as a method for providing digital signatures.
The Merkle tree provides a data structure for verifying individual records.
But Merkle was not the only one to help set the stage for Blockchain.
David Chaum described a vault system for establishing, maintaining and trusting computer systems by mutually suspicious groups in his 1982 Ph.D. dissertation for the University of California, Berkeley.
This was a system that embodied many of the elements that make up a blockchain.
Chaum is also credited with inventing digital cash, and in 1989, he founded the DigiCash corporation.
In 1991, Stuart Haber and W. Scott Stornetta published an article about timestamping means (it's a digital record of the time of occurrence of a particular event) digital documents.
The article proposed a solution for preventing users from backdating or forward-dating electronic documents.
The goal was to maintain complete privacy of the document itself, without requiring record-keeping by a timestamping service.
In 1992 Haber and Stornetta updated the design to incorporate Merkle trees, which enabled multiple document certificates to live on a single block.
During these early years, there was plenty of other activity that also helped make blockchain possible.
For example, this era saw the rise of the P2P network, a concept popularized in 1999 by the now defunct Napster.
Some would argue that Napster was not a true P2P network because it used a centralized server.
However, the service still helped breathe life into the P2P network, making it possible to build a distributed system that could benefit from the compute power and storage capacity of thousands of computers.