The earliest origin of hard tissues in the Eukaryotic Domain can now be traced back to the mid-Neoproterozoic thanks to Phoebe Cohen, her coauthors, and spectroscopy.
Carbon. Calcium. Phosphorus. These three ingredients are used to build the bones of every living animal. And every extinct animal. Indeed, the first bones were also built using carbon, calcium and phosphorus, but the bones of animals are not the only hard tissues made using these key ingredients. Some living algae also build phosphatic skeletons. And so did some extinct algae, including three mid-Neoproterozoic (717–812 Ma) species from Canada.
Phoebe Cohen and colleagues (including J. William Schopf) recently presented the “…earliest compelling evidence of biologically controlled eukaryotic biomineralization known in the fossil record…” Eukaryotes are organisms whose cells contain complex structures enclosed within membranes, like you, me and trees, and unlike bacteria (which are prokaryotes). The evidence for biomineralization of the algal scales includes traces of carbon, calcium and phosphorus detected using energy-dispersive x-ray fluorescence spectroscopy. These three elements are remnants of ancient phosphatic tissues. The chemistry of phosphatic tissues can be mimicked by minerals that form during burial, however, but Cohen and colleagues state that “…none of the scales… are deformed or show any evidence of either phosphate replacement or secondary apatite overgrowths…” Another possibility for the mineralised structures is replacement of calcium carbonate with calcium phosphate over time, but “…the possibility that these fossils were originally composed of calcium carbonate can be discounted due to the absence of (1) carbonate pseudomorphs, (2) any carbonate signal in the Raman spectra, and (3) cast and mold structures characteristic of phosphate replacement…” So, the earliest origin of hard tissues in the eukaryotic Domain can now be traced back to the mid-Neoproterozoic thanks to spectroscopy.
Cohen PA, Schopf, JW, Butterfield NJ, Kudryavtsev AB, Macdonald FA, 2011. Phosphate biomineralization in mid-Neoproterozoic protists. Geology 39, 539-542.
Image modified from Wikimedia Commons
Artists impression of the Mars rover ‘Curiosity’ using its LIBS system to analyse rocks.
The next Mars Rover in the launch schedule is a mobile laboratory called ‘Curiosity’. One of the aspirations for Curiosity’s mission is to study the habitability of Mars, with a view towards ancient life. From the Mars Science Laboratory website, “…The rover will analyze dozens of samples scooped from the soil and drilled from rocks. The record of the planet’s climate and geology is essentially “written in the rocks and soil” — in their formation, structure, and chemical composition. The rover’s onboard laboratory will study rocks, soils, and the local geologic setting in order to detect chemical building blocks of life (e.g., forms of carbon) on Mars and will assess what the martian environment was like in the past…”. So, Curiosity will be a Martian paleontologist.
The instrument suite onboard the SUV-sized Curiosity would happily replace the analytical facilities of most geochemistry labs. Curiosity is not carrying vibrational spectroscopic instrumentation (…that will have to wait for ExoMars), but it does have something equally awesome: LIBS. Light-induced breakdown spectroscopy uses a laser (in this case, a neodymium:potassium gadolinium tungstate solid state laser) to atomise a sample. Think Death Star vs. Alderaan. The atomised samples become highly excited, which means electrons jump to higher energy levels. Vacancies in electron shells are eventually refilled: electrons at higher energy levels lose energy and slot into lower energy levels. The energy that is lost during this transition is a photon, with a wavelength characteristic of the atom where all of this is taking place. So, if you collect the photons that are emitted when you atomise your sample, you can assess the composition of the sample you atomised. Think Grand Moff Tarkin with a Polaroid. What makes this particularly awesome, however, is that Curiosity can use its LIBS system on samples that are up to 7m away.
How does this make Curiosity a paleontologist? The fossil remains of life on Earth have very distinct chemistries covering lighter (hydrogen, carbon, oxygen, nitrogen) and heavier elements (calcium, iron). The LIBS system onboard Curiosity can detect most elements, and might give us our first hard evidence for extraterrestrial life.
Image from NASA