And then there is the Dinosaur Institute, which has many fossils older than million years. And even that, while definitely old, is nothing compared to some of the specimens in Invertebrate Paleontology. They have a few fossils that are billions of years old! The picture above is one of the stromatolites in the Invertebrate Paleontology Collections — by far the oldest fossils we have. This particular one — about 3.
The stripes were formed by layer after layer of cyanobacteria, which formed mounds over time. Stromatolites still exist today on the coasts of places like Australia. William Schopf. He collected the rock in which the fossils were found in from the Apex chert deposit of Western Australia, one of the few places on the planet where geological evidence of early Earth has been preserved, largely because it has not been subjected to geological processes that would have altered it, like burial and extreme heating due to plate-tectonic activity.
Critics argued they are just odd minerals that only look like biological specimens. However, Valley says, the new findings put these doubts to rest; the microfossils are indeed biological.
Using a secondary ion mass spectrometer SIMS at UW—Madison called IMS — one of just a handful of such instruments in the world — Valley and his team, including department geoscientists Kouki Kitajima and Michael Spicuzza, were able to separate the carbon composing each fossil into its constituent isotopes and measure their ratios.
Isotopes are different versions of the same chemical element that vary in their masses. Their Cto-C ratios are characteristic of biology and metabolic function. John Valley, professor of geoscience, is pictured in his office in Weeks Hall. Based on this information, the researchers were also able to assign identities and likely physiological behaviors to the fossils locked inside the rock, Valley says.
UW—Madison geoscience researchers on a field trip to the Apex Chert, a rock formation in western Australia that is among the oldest and best-preserved rock deposits in the world. Courtesy of John Valley. The study builds on earlier achievements at WiscSIMS to modify the SIMS instrument, to develop protocols for sample preparation and analysis, and to calibrate necessary standards to match as closely as possible the hydrocarbon content to the samples of interest.
In preparation for SIMS analysis, the team needed to painstakingly grind the original sample down as slowly as possible to expose the delicate fossils themselves — all suspended at different levels within the rock and encased in a hard layer of quartz — without actually destroying them. Spicuzza describes making countless trips up and down the stairs in the department as geoscience technician Brian Hess ground and polished each microfossil in the sample, one micrometer at a time.
Each microfossil is about 10 micrometers wide; eight of them could fit along the width of a human hair. These microbes lived in large mats, which produced sticky mucus that trapped sand grains and minerals.
As the bacteria continued growing, they moved upwards, leaving layers of minerals in their wake. Over time, those minerals hardened into domes and mounds. Until now, the oldest known stromatolites came from Western Australia, and were 3. They represented the earliest convincing evidence of life on Earth. And the structures that Nutman, Bennett, and Friend discovered in Greenland are 3. If the trio are reading them correctly, and they really were produced by bacteria, then they are easily the oldest fossils ever found.
If you condense the entire history of the Earth into a single calendar year, then the bacteria that created the Greenland fossils were alive in the second week of March. And since they were already sophisticated, capable of forming large colonies, life itself must have arisen much earlier, perhaps sometime in mid-February.
Stromatolites have long been controversial. Natural processes can produce structures that look very similar to stromatolites, and many scientists have become embroiled in long debates about whether a given bit of rock was really the work of microbes.
It seemed unlikely that researchers would find older ones, given that there are few other sites on Earth where older rocks actually exist. Western Greenland—and especially a coastal site called the Isua Greenstone Belt —is an exception, but still a problematic one.
They seemed unlikely to preserve the clean layers and shapes that make stromatolites so distinctive. At first, Nutman and others searched the Greenland rocks for alternative signs, like chemical signatures that could betray the activity of living things.
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