Humans are 400,000 yrs older than previously thought

So it turns out that humans existed 400,000 years before than previously believed.

Recently found in the Afar region of Ethiopia, the earliest known record of the genus Homo, the human genus, represented by a lower jaw with teeth, dates to between 2.8 and 2.75 million years ago, according to an international team of geoscientists and anthropologists.

They also dated other fossils to between 2.84 and 2.58 million years ago, which helped reconstruct the environment in which the individual lived.

Erin N. DiMaggio, research associate in the department of geosciences, Penn State, said that the record of hominin evolution between 3 and 2.5 million years ago is poorly documented in surface outcrops, particularly in Afar, Ethiopia.

The researchers dated the recently discovered Ledi-Geraru fossil mandible, known by its catalog number LD 350-1, by dating various layers of volcanic ash or tuff using argon40 argon39 dating, a method that measures the different isotopes of argon and determines the age of the eruption that created the sample.

DiMaggio, lead author on the paper, said that they were confident in the age of LD 350-1, as they used multiple dating methods including radiometric analysis of volcanic ash layers, and of which show that the hominin fossil was 2.8 to 2.75 million years old.

Other fossils found in this area include those of prehistoric antelope, water dependent grazers, prehistoric elephants, a type of hippopotamus and crocodiles and fish. These fossils fall within the 2.84 to 2.54 million years ago time range.

The fossils suggest that the area was a more open habitat of mixed grasslands and shrub lands with a gallery forest-trees lining rivers or wetlands. The landscape was probably similar to African locations like the Serengeti Plains or the Kalahari. Some researchers suggest that global climate change intensifying roughly 2.8 million years ago resulted in African climate variability and aridity and this spurred evolutionary changes in many mammal lines.

The results are presented in the online issue of Science Express.