Soil suggests early humans lived in forests instead of grasslands

July 11, 2001

CHAMPAIGN, Ill. -- Carbon isotope evidence in almost 6-million-year-old soils suggests that the earliest humans already were evolving in - and likely preferred - humid forests rather than grasslands, report a team of scientists working in Ethiopia.

The discovery challenges long-held beliefs, beginning with Darwin, that humans did not evolve into upright beings and thrive until expanding tropical grasslands forced our chimpanzee-like ancestors out of dwindling forests about 4 million to 8 million years ago.

Hominid fossil sites from the later Pliocene period (2.5 million to 4.2 million years ago) previously had been found in savanna habitats. Researchers had been confident that the slightly earlier hominids living in the late Miocene also would be found in the savanna.

"The expectation was that we would find hominids in savanna grassland sites that date back to about 8 million years ago. That hasn't happened," said anthropologist Stanley H. Ambrose of the University of Illinois. "All older hominids have been found in forested environments."

The analysis was of fossil soils from paleontological sites in the Middle Awash region of Ethiopia's rift valley, where the remains of a new subspecies of Ardipithecus ramidus have been discovered. They date to the late Miocene period (5.4 million to 5.8 million years ago). Scientists from four institutions report their findings in a pair of papers that appear in the July 12 issue of the journal Nature.

Ambrose collected fossil soil samples from the layers containing the newly found hominids. One of the fossils was found by team member Leslea Hlusko, also a UI professor of anthropology. Ambrose performed geochemical studies on the samples in his UI laboratory.

The region where the fossils were found is now a hot, dry semi-desert occupied by nomadic camel herders. At the time the area formed, it was higher in elevation, cooler, wetter and more forested.

Ambrose's geochemical technique allows for an environmental reconstruction of soils by examining the carbonate nodules (caliche) in the samples. The nodules reflect the types of plants that grew in the soils. Tropical grasses contain more of the heavy isotope of carbon than do trees, shrubs and leafy plants. The nodules from these late-Miocene hominid fossil sites contain low levels of carbon 13, which is consistent with trees and woody plants. They also contain oxygen isotope ratios that are indicative of a cool, humid climate. "These hominids were living in the forest, despite the fact that grasslands were available," Ambrose said.

The new findings, he said, require a fundamental reassessment of models that invoke a significant role for global climatic change and/or adaptation to savanna habitats in the origin of hominids.
-end-
Ambrose's findings appear in a paper cowritten with seven other researchers: Tim White, Yohammes Haile-Selassie and Paul R. Renne of the University of California at Berkeley; Giday WoldeGabriel and Grant Heiken of the Los Alamos National Laboratory in New Mexico; William K. Hart of Miami University in Oxford, Ohio; and Berhane Asfaw of the Rift Valley Research Service in Addis Adaba, Ethiopa.

The National Science Foundation and the University of Illinois Research Board provided funding for Ambrose's research.

University of Illinois at Urbana-Champaign

Related Carbon Articles from Brightsurf:

The biggest trees capture the most carbon: Large trees dominate carbon storage in forests
A recent study examining carbon storage in Pacific Northwest forests demonstrated that although large-diameter trees (21 inches) only comprised 3% of total stems, they accounted for 42% of the total aboveground carbon storage.

Carbon storage from the lab
Researchers at the University of Freiburg established the world's largest collection of moss species for the peat industry and science

Carbon-carbon covalent bonds far more flexible than presumed
A Hokkaido University research group has successfully demonstrated that carbon-carbon (C-C) covalent bonds expand and contract flexibly in response to light and heat.

Metal wires of carbon complete toolbox for carbon-based computers
Carbon-based computers have the potential to be a lot faster and much more energy efficient than silicon-based computers, but 2D graphene and carbon nanotubes have proved challenging to turn into the elements needed to construct transistor circuits.

Cascades with carbon dioxide
Carbon dioxide (CO(2)) is not just an undesirable greenhouse gas, it is also an interesting source of raw materials that are valuable and can be recycled sustainably.

Two-dimensional carbon networks
Lithium-ion batteries usually contain graphitic carbons as anode materials. Scientists have investigated the carbonic nanoweb graphdiyne as a novel two-dimensional carbon network for its suitability in battery applications.

Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.

Investigation of oceanic 'black carbon' uncovers mystery in global carbon cycle
An unexpected finding published today in Nature Communications challenges a long-held assumption about the origin of oceanic black coal, and introduces a tantalizing new mystery: If oceanic black carbon is significantly different from the black carbon found in rivers, where did it come from?

First fully rechargeable carbon dioxide battery with carbon neutrality
Researchers at the University of Illinois at Chicago are the first to show that lithium-carbon dioxide batteries can be designed to operate in a fully rechargeable manner, and they have successfully tested a lithium-carbon dioxide battery prototype running up to 500 consecutive cycles of charge/recharge processes.

How and when was carbon distributed in the Earth?
A magma ocean existing during the core formation is thought to have been highly depleted in carbon due to its high-siderophile (iron loving) behavior.

Read More: Carbon News and Carbon Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.