The 2.8 million-year-old example is 400,000 years more established than specialists believed that our kind initially rose.
The revelation in Ethiopia proposes environmental change impelled the move from tree tenant to upright walker.
The leader of the exploration group revealed to BBC News that the discover gives the primary knowledge into "the most essential moves in human development".
Prof Brian Villmoare of the University of Nevada in Las Vegas said the revelation makes a reasonable connection between a notable 3.2 million-year-old hominin (human-like primate) found in a similar range in 1974, called "Lucy".
Could Lucy's benevolent – which had a place with the animal categories Australopithecus afarensis – have advanced into the primary primitive people?
"That is the thing that we are contending," said Prof Villmoare.
In any case, the fossil record between the day and age when Lucy and her kinfolk were alive and the development of Homo erectus (with its moderately substantial mind and humanlike body extents) two million years back is meager.
The 2.8 million-year-old lower jawbone was found in the Ledi-Geraru look into region, Afar Regional State, by Ethiopian understudy Chalachew Seyoum. He disclosed to BBC News that he was "staggered" when he saw the fossil.
"The minute I discovered it, I understood that it was imperative, as this is the day and age spoke to by couple of (human) fossils in Eastern Africa."
The fossil is of the left half of the lower jaw, alongside five teeth. The back molar teeth are littler than those of different hominins living in the range and are one of the elements that recognize people from more primitive progenitors, as per Professor William Kimbel, chief of Arizona State University's Institute of Human Origins.
"Already, the most established fossil ascribed to the variety Homo was an upper jaw from Hadar, Ethiopia, dated to 2.35m years prior," he revealed to BBC News.
"So this new revelation pushes the human line back by 400,000 years or somewhere in the vicinity, near its probable (pre-human) predecessor. Its blend of primitive and propelled highlights makes the Ledi jaw a decent transitional shape amongst (Lucy) and later people."
A PC reproduction of a skull having a place with the animal types Homo habilis, which has been distributed in Nature diary, shows that it might well have been the transformative relative of the species reported today.
The specialist included, Prof Fred Spoor of University College London disclosed to BBC News that, taken together, the new discoveries had lifted a shroud on a key period in the development of our species.
"By finding another fossil and re-investigating an old one we have really added as far as anyone is concerned of our own transformative period, extending over a million years that had been covered in secret," he said.
Environmental change
The dating of the jawbone may help answer one of the key inquiries in human advancement. What brought about some primitive precursors to move down from the trees and make their homes on the ground.
A different review in Science indicates that an adjustment in atmosphere may have been an element. An investigation of the fossilized plant and creature life in the range proposes that what had once been lavish timberland had turned out to be dry prairie.
As the trees cleared a path for immeasurable fields, old human-like primates found a method for abusing the new ecological specialty, creating greater brains and turning out to be less dependent on having enormous jaws and teeth by utilizing instruments.
Prof Chris Stringer of the Natural History Museum in London portrayed the revelation as an "issue on everyone's mind".
He says the new species plainly shows the most punctual stride toward human attributes, yet proposes that a large portion of a jawbone is insufficient to tell exactly how human it was and does not give enough confirmation to recommend that it was this line prompted to us.
Picture inscription The jawbone was discovered near the zone where Lucy was found
He takes note of that the rise of human-like attributes was not remarkable to Ethiopia.
"The human-like components appeared by Australopithecus sediba in South Africa at around 1.95 million years prior are probably going to have grown autonomously of the procedures which delivered (people) in East Africa, demonstrating that parallel inceptions are a particular plausibility," Prof Stringer clarified.
This would propose a few distinct types of people existing together in Africa around two million years back with just a single of them surviving and inevitably advancing into our species, Homo sapiens. It is as though nature was trying different things with various adaptations of the same transformative setup until one succeeded.
Prof Stringer included: "These new reviews abandon us with a considerably more perplexing picture of early people than we suspected, and they provoke us to consider the very meaning of what it is to be human. Is it accurate to say that we are characterized by our little teeth and jaws, our vast cerebrum, our long legs, instrument making, or some mix of these qualities?"
