A 650-million-year-old fossil from Kazakhstan. Top: optical image of fossil cyanobacterium. Middle: confocal optical image of the same fossil. Bottom L: close-up of section of confocal optical image. Bottom R: Raman chemical image of same boxed region
Credit: Dr. J. William Schopf/UCLA
Scientists have produced the first-ever three-dimensional images of 850-million-year-old microscopic fossils using preexisting laser technology.
They don't even have to break open the rocks.
Hard to photograph
Geologists have struggled to study these ancient single-celled organisms because their small size—about one-fiftieth the diameter of a human hair—makes them difficult to find and photograph.
Previous 2-D images of the little critters left researchers with room for subjectivity about their size and shape. With the newly applied techniques of confocal laser scanning microscopy (CLSM) and Raman spectroscopy, scientists can now search inside the rocks for signs of life.
The research, led by University of California, Los Angeles paleobiologist J. William Schopf, was published in the January issue of Astrobiology.
"We can now see, in 3-D, inside rocks, very tiny microscopic filaments in all their glory," Schopf told LiveScience. "We see their chemistry and morphology, and can compare that with modern organisms."
Originally developed to look at the insides of living cells, CLSM creates a high-resolution 3-D image of the specimen. Raman spectroscopy, used primarily by chemists, visualizes the molecular and chemical structure of microorganisms in three dimensions. Raman spectroscopy helps prove whether fossils are actually biological or just very old rock bits, said Andrew Czaja, a UCLA graduate student.
"The method proves that these fossils are made up of mostly carbon, which all organisms are mostly made of," Czaja said. "Now we can show where carbon matches the morphology."
Both techniques involve pointing a laser at a fossil. The carbon fluoresces, or glows, naturally when hit by a laser. By recording all of the points of fluorescence, scientists can connect the dots and create a 2-D map of the fossil. From the stacked collection of 2-D images, a computer generates a 3-D view, which can be manipulated to see the fossil from any angle—a feat impossible before now.
Unlike other magnifying techniques that rely on high-magnification microscopes, the new noninvasive procedures ensure that microfossil specimens are preserved in rocks and not damaged or contaminated.
The next rage?
The techniques work well together, Czaja said. While Raman spectroscopy gives chemical information in 3-D, CLSM is 50 times faster and its images are 3 times sharper. The research team used CLSM as a filtering device to determine whether a fossil warranted a time-consuming chemical analysis.
The UCLA team produced images of fossil bacteria 650 million to 850 million years old. Their ongoing projects will study more ancient fossils, and could help better understand the earliest life on Earth.
Someday, Schopf said, the same techniques will be applied to studying rocks from Mars.
"I don't think any other lab in the world has both of these instruments," said Schopf. "But they will now."