The seeds of life were first sown 3.5 billion years ago in a shallow swamp in Swaziland in the south of Africa.
It is a place geologists call Figtree, where the waters of the Umbilizi River wash through a rolling countryside on the way to Mozambique and the Indian Ocean. Life began at Figtree as microscopic one-celled creatures that rapidly divided, were spread around the world by the winds and evolved to form a soup of blue-green algae that persisted as the only life on Earth for more than two billion years.
These conclusions come from an article that will appear in Science magazine later this month, when Harvard University paleontologist named Elso Barghoorn will announce that he has found microscopic fossils at Figtree that go back 3.5 billion years.
"There may be fossils in other parts of the world older than Figtree," Barghoorn said the other day in his laboratory at Harvard's Herbaria Museum, "but we haven't found any. So Figtree looks like the bottom of the pile."
What Barghoorn and a Harvard graduate student named Andrew Knoll found at Figtree, in this slices of hard black rock called chert, were swarms of tiny fossilized creatures that are almost surely primitive forms of algae.
All single-cell spheres, the fossils were so well preserved they can be seen dividing under the microscopic. Some had just divided when they were trapped by minerals solidifying in the ancient swamp and turned into fossils. Barghoorn has slides that show two fossils spheres after cell division, side by side in the rock.
The fossils themselves can't be dated but the age of the rocks they're sealed in can be fixed with uncanny precision. Figtree's age has been reached using the same radioactive methods that were used to date the Apollo moon rocks. Barghoorn says there is no question the Figtree fossils are 3.5 billion years old, meaning they are 1.2 billion years older than any fossils found before.
"Figtree is a piece of the early Earth," Barghoorn said. "Keep in mind that 3.5 billion gets you back to where you only have 1 billion more to the beginning" of the earth 4.6 billion years ago.
The Figtree find seems the most dramatic of scores of recent discoveries of evidence of what scientists call Pre-Cambrian life (more than 510 million years old). In the last 12 years, after more than 100 years of having no proof for fossil life before the Cambrian period, scientists have found no fewer than 36 well-preserved microfossils in Greenland, Australia, Siberia, Soviet Asia, the Grand Canyon and the mountains of Utah. Half of these new microfossils were found in the last two years.
"There is an intense search all over the world for Pre-Cambrian life right now," said Dr. J. William Schopf, a 35-year-old paleontologist at UCLA who has made many of the most recent finds. "The field is in an uproar, in ferment."
Out of this ferment, geologists have identified at least 12 ancient rockbeds near lakes and oceans they call "stromatolites." Looking like clumps of mud that form along shorelines when the tide runs out, stromatolites are really the leftover limestone excretions of algae and bacteria that were here on Earth before animals.
Few stromatolites are forming today because animals eat the organisms that make them. Stromatolites are not fossils themselves because they erase the organisms that make them. Nonetheless, the ancient dozen identified today as Pre-Cambrian are considered a part of the fossil record.
Stromatolites close to 2 billion years old have been found in Australia, Canada and Soviet Union. The oldest stromatolite is in Rhodesia and is 3 billion years old, which means the algae and bacteria that produced them were alive in Rhodesia at the same time.
When geologists talk of the pre-Cambrian, they mean roughly the first 4 billion years of the earth's history. The Cambrian period began about 570 million years ago, and is regarded by geologists as marking the beginning of the earth's most recent history.
It is in Cambrian and younger rock that all the fossils have been found that can be seen with the naked eye. The oldest Cambrian fossils are the smallest, the remains and tracks of soft-bodied animals like worms and jellyfish that for years were the oldest evidence of life on earth.
Charles Darwin worried why nobody found fossils in rock older than Cambrian. In his monumental book "The Origin of Species," Darwin wrote that he would never be comfortable with his own theory of evolution until signs were found of a simpler life that grew to the more complex forms he knew in the Cambrian. It was as if life suddenly began in the forms of worms and jellyfish, with nothing simpler before them.
In 1951 a mineralogist named Stanley Tyler was prospecting for iron along the Michigan shores of Lake Superior when he came upon ancient coal deposits that contained what he thought were microscopic plants.
Tyler showed the coal to MIT geology Chairman William Shrock, who thought the "plants" looked like the fungus that grows in a jelly jar left open too long. Shrock suggested Tyler seek our a young Harvard botanist who'd served in Panama in World War II seeking ways of protecting binoculars against the fungi eating them away in the South Pacific.
The botanist was Elso Barghoorn, who teamed up with Tyler in a search along the shores of Lake Superior for whatever was wrinkling the ancient coal. The search took them to the Canadian side of the lade, where they found black shales and cherts that appeared to be imprinted with colonies of blue-green algae.
A diamond saw was used to cut slices of the rock so thin that light passed through them. Borghoorn took three of the most promising slices back to Harvard, where he looked at them under his microscope.
"I almost fell off my chair," Barghoorn recalled. "I realized that what I was looking at were organisms that looked exactly like fossil algae."
Tyler in Wisconsin and Barghoorn in Massachusetts worked tirelessely to prove what they had. They cut more than 800 thin sections of the flintlike black chert they found in Canada, in a geological formation appropriately named Gunflint.
The two scientists made slides of all the thin sections they had so painstakenly cut. They put microscopic sections of the microfossils to the torch to see if they'd burn. Fossils burn. Mineral that looks like a fossil won't burn.
Their efforts were hampered by distance and personal problems. Tyler's wife fell ill with cancer and work suffered. She died and work stopped. They announced a preliminary finding and where the find was not greeted with skepticism it was ignored - until Dr. Preston Cloud from the University of California at Santa Barbara went to Gunflint and began finding some of the same fossils.
Tyler died in 1964 but by then Barghoorn was caught in a race with Cloud to publish the Gunflint findings. Then, just before Tyler's death, a well-known MIT scientists named Patrick Hurley independently pronounced the Gunflint rock to be 2 billion years old, proving the fossils Pre-Cambrian without a doubt.
"It suddenly became apparent we were dealing with a complex assemblage of organisms 2 billions years old." Barghoorn said "The whole story began to fall into place."
Fall in it did. Barghoorn published an exhaustive paper on Gunflint in February, 1965, with Tyler his post-humous co-author. They beat Cloud to publications by three months.
In the 12 years that followed, paleontologists (they study the history of life) have been busier than they've been at any time in the last 100 years. They've found microfossils in Canada, Alaska and Arizona that are 850 millions years old. Fossils were found in Australia that were 900 millions, 1 billion and almost 1.2 billion years old.
Fossils were found at dismal Lakes in the Canadian Arctic that are 1.2 billion years old and in southern India that are 1.4 billion years old. At least seven fossils more than 1 billion years old have been uncovered in the Soviet Union.
Three new finds have been made in Australia that date the start of life Down Under at 1.7 billion years. A find has been made in the Transvaal in South Africa that takes life back 2.3 billion years. The transport fossils were the oldest until Barghoorn's Figtree find.
None of this discovery has been easy. Bulldozers were needed to get at the coal deposits that led Tyler and Barghoorn to Gunflint. The coal formation was seven miles from the nearest town and it took weeks in the field for the two men to scratch out samples. Gunflint was even more remote. It was 20 miles from any town.
Rocks in Rhodesia suspected of being at least as old as Figtree are "politically inaccessible," says Barghoorn, who has hacked at "accessible" ancient rock in Rhodesia that's suffered so much from volcanic heat that the carbon (where the fossils would be) in the rock is pure graphite, which forms at 7,500 degrees.
"The older the rock get the harder they are to decipher," explains UCLA's BIll Schopf. "There are fewer and fewer rocks that haven't been recycled by time and fewer and fewer fossils well enough preserved to identify."
Nonetheless, the knowledge gleaned from the surge in microfossil work is reaching landslide proportions. Major differences have been observed between fossil algae cells and the cells of modern algae. Why is that? At the same time, the 700 million-year old fossils of soft-bodied animals like worms and jelly-fish turning up in all this work resemble precisely the worms and jellyfish living in Earth today. Why haven't they changed with time?
It's no accident, says Johns Hopkins University's Dr. Robert Bakker, that paleontology is being the reborn at the same time the science of molecular biology (submicroscopic genetics) is emerging. Both deal with the evolution and control of cells. Bakker says both will contribute to the curing of cancer and the feeding of world populations.
None of the microfossils found is identical to another. The oldest fossils are the smallest, the least complex. The youngest are the largest and the most intricate under the microscope.
No great surprise, this trend confirmed Darwin's theory of evolution very nicely at the same time that it's telling scientists something about the early history of Earth. The primitive blue-green algae that dominated Earth for almost 2 billion years thrived without oxygen. The more complex algae that began to appear almost 2 billion years ago seem to have needed some oxygen, suggesting that oxygen began to enrich the atmosphere about the same time.
Abundant microfossils 1.5 billion years old were found in one of Australia's richest mineral deposits, suggesting the animal or fossil life may have had something to do with the copper, lead and zinc that's been found there. A man and wife paleontologists team named Oehler spent three recent years in Australia studying the possibility of just such a role.
"There's no evidence that algae and bacteria participated in forming the minerals" said Dr. John Oehler, who together with his wife, Dorothy, now works for Continental Oil Co. in Ponca City, Okla. "But we do think they were responsible for maintaining the non-oxidizing conditions in the soil that allowed the preservation of these minerals.
Dr. Cloud makes a somewhat similar suggestion about iron reserves. Earth stopped making iron about 1.8 billion years ago, suggesting two things to Cloud. First, free oxygen began to build up in the atmosphere and iron began to oxidize away from its metallic state. Second, microscopic life began to turn more complex and depend on oxygen for its survival.
What's next in what UCLA's Schopf regards as "just the beginning" of the renaissance in paleontology?
Most paleontologists talk of a search for the fossils marking the transition of life from the primitive form to the complex one that exploded through life at the start of the Cambrian period 570 million years ago. They talk of finding the first fossils of the eukaryotic cell, the complex cell with a nucleus, with chromosomes and the kind of chemistry and wall structure found in life thriving today.
The microfossils found in the last 10 years were built from cells called prokaryotic, without nucleus, without chromosomes to sexually reproduce. When and how did these simple cells cross over and become (the word literally means "true nut") eukaryotic? Put another way: When did sex begin?
"Modern biologists," Oehler said, "regard this transition as the single most important step in evolution. To understand it will be a major milestone in scientific research."
NEXT: Life outside of Earth