Written by Mark Teutsch of Deerfield Academy
Mark was one of the faculty sent from Deerfield Academy to attend our 2011 Curriculum Design Course pictured above, 6th person from the left. This article was inspired by his walks down the beach during his stay and in particular the marine tubeworm castings that are abundant along the coastline.
Life Erupts from Geology
First introduced to LUCA some twenty years ago, I now wonder what’s caused me to again take up interest. Why should I care about where she came from, her energy and those she’s given rise to?
For many reasons, I took great benefit from a journey south of the boarder, to Costa Rica. There, at CERENAS on the beach I stumbled upon a biological artifact with appearance of a lipstick container. Afterwards, in the weeks that followed my return to Deerfield, I really began to wonder, was the artifact in any way associated with LUCA, or her descendants?
The inspiring place, the Nicoya Peninsula in Western Costa Rica, possesses a similarly exotic allure as LUCA. Twenty four hundred miles southwest of campus, Costa Rica is a place that, when considering our most recent ice age, shares a curious geological connection with Deerfield. Five major periods of ice ages have affected Earth, the most recent beginning 2.6 million years ago (MYA), coinciding with formation of Costa Rica and greater Central America. Geologically, New England is older than Costa Rica, dating back to a time earlier than the formation of Pangaea 250 MYA. Yet, it’s believed that a trigger for the last ice age that carved up Deerfield was formation of the Isthmus of Panama.
The Isthmus of Panama began forming around 20 MYA when the Western Caribbean plate overrode, or subducted, the Pacific Ocean’s Cocos plate (Figure 1). Building pressures within the mantle from the subduction caused release and rise of lava and gasses underneath the Caribbean plate and along the Middle American Trench. Such events produced volcanoes that erupted until peaks ultimately emerged above sea level, connecting North and South America. Prior to formation of the isthmus, warm water currents running north along Eastern South America flowed through the Caribbean, ultimately dumping the warmth into the Pacific Ocean. However, with an emerging Central America acting as a land bridge, warm ocean waters got deflected north, reinforcing the Gulf Stream that brings warmth to North American East Coast.
Ice ages require two conditions, cool continental temperatures and air moisture for falling snow. There’s speculation that increased air moisture resulted when the warm water that had dumped into the Pacific was diverted into the North Atlantic. It’s the Pleistocene ice age that provides us with striking geological structure observed in Deerfield today. To me, this seems a curious connection between Costa Rica and Deerfield.
In perspective of time, formation of the Isthmus of Panama occurred 2.6 MYA and corresponds with Australopithecus Lucy who roamed Africa. Predawn at CERENAS, it was common to hear vocal troops of Howler Monkeys that caused wonder about their language, and the developing language of our ancestors. Of our ancestors, Lucy and LUCA, the tag line used by ancestory.com seems appropriate enough, you don’t have to know what you’re searching for when you start, just start searching.
LUCA is an acronym for the last universal common ancestor, the hypothesis for her existence provoked by the distinguished Deerfield alum Carl Woese’s work. Biology asks questions about the nature and diversity of life. Life is defined as possessing metabolism, homeostasis, the abilities to reproduce and adapt to environment in successive generations. When considering LUCA, how did such basic requirements for life come together 3.5 billion years ago on young Earth?
Biologists studying origin of life have interest in the thermodynamics (sometimes called the science of desire) that would favor assembly of RNA/protein precursors on young Earth. Questions are asked whether supporting origin of life environments may have been extraterrestrial, terrestrial clays, primordial soups or deep-sea hydrothermal vents. Travel to CERENAS and wandering along the shoreline led me to reconsider the developing story surrounding life’s possible emergence from deep-sea hydrothermal vents.
Less than fifty years ago, when the cattle ranch that is now CERENAS was even more remote, scientists thought life could not be sustained at temperatures much above 50° Celsius. However, in 1969 thermophilic (heat loving) bacteria were discovered in a Yellowstone geyser and soon thereafter at deep ocean hydrothermal vents like those found within a few miles of Costa Rica. These bacteria not only survived, but thrived at temperatures around 100° Celsius, and the first thermophilic organism identified named Thermus aquaticus. As a young biologist in the 1970’s, Woese encountered a long period of great controversy, followed by scientific fame, for defining Archaea, the most ancient domain of life (Figure 2). Archaea proliferate along hydrothermal vent environments, ocean trenches and geological subduction zones. Archaea have sustained such vast deep-sea life communities because they are metabolically independent of solar energy, instead deriving energy chemosynthetically from minerals and gases (hydrogen sulfide, hydrogen and carbon dioxide) emerging from ocean vents. Many Archaea are also oxygen independent anaerobes, as was LUCA and her earliest descendents of life.
At deep-sea vents, chemosynthetic life (Archaea) attracts organisms that graze upon them, forming predator/prey food-chain relationships. On the beach, there, along the Playa Ario beach, are abundant remains reminiscent of lipstick canisters that are washed up, scattered among shells, driftwood and plastic. On the ocean floor, tubeworms inhabit the canisters and hold a bizarre symbiotic relationship with the ancient Archaea. Lacking any mouth or digestive tract, tubeworms absorb nutrients directly into their tissues from Archaea that live inside the cylindrical tube organism. With red ruse appearance when alive, tubes protrude like lipstick from chitin canisters that are based near benthic rock vents. Production of hemoglobin is what gives the organisms their red ruse appearance as the iron-core molecule latches onto hydrogen sulfide expelled from deep hydrothermal vents. When molecularly bound, the hemoglobin/hydrogen sulfide complex is transferred from tubeworm to Archaea colonies harbored and protected within the organism’s core. In return, the chemosynthetic Archaea nourish protector and provider with small carbon compounds, similar to pyruvate, used to feed tubeworm metabolic cycles.
The gentle reader may by now be wondering if these threads will ever be weaved together. How do remains, aesthetically beautiful as they are (Figure 3), of chitin based tubeworm colonies on a Costa Rican beach connect in any way with the last universal common ancestor – that is, the first organism on Earth? Directly they don’t; but, tubeworms are a kind of living fossil whose distant ancestors may have been players in origin of life story.
Woese, from his phylogenetic analysis of ribosomal RNA, and others, have approached LUCA top down. The reasoning goes: since photosynthesis is only observed in a small subset of bacteria, it’s unlikely that LUCA was photosynthetic. All living things are composed of cells, have genes made of DNA and encode proteins using universal code for particular amino acids. Also, life uses a common energy currency, adenosine triphosphate (ATP), capable of paying for work done in cells. Last but not least, life shares common core metabolic reactions, the heart of which is known as Krebs cycle. Yet, it’s a long top-down drop from having a membrane bound replicator that’s driven by Krebs and uses ATP to envisioning de novo assembly of packaged molecules that can affect such functions.
Recently (reviewed in 3), Mike Russell proposed that, “Life emerged from growing aggregates of iron sulfide bubbles containing alkaline and highly reduced hydrothermal solutions. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from the oceanic spreading centers 4 billion years ago.” These ideas were visionary because early in the 21st century scientists aboard the submersible Atlantis discovered just this type of vent. There, delicate white carbonate and aragonite structures reach upward. Tubeworm like, the porous structures contain ubiquitous microscopic compartments that, just like present day cells, can concentrate molecules exploiting chemical disequilibrium and are presently teeming bacterial nests. Moreover, just miles from the CERENAS Ranch, in the Pacific Ocean along the Galapagos rift and not far from the same Galapagos Islands that inspired Darwin to offer hints into the origin of species and life itself, the US Naval submersible Alvin descended to study oceanic hydrothermal vents and found giant tubeworms living at extreme depths, temperatures, pressures and acidic conditions.
Approaching LUCA from the bottom up, many are asking these days if the Krebs cycle isn’t the core of life. From this core, like gears on a Swiss watch, biological cycles spin forward and backward, connected to other biochemical pathways that regulate levels of lipids, proteins, carbohydrates and nucleic acids. Normally in the forward direction, the Krebs cycle consumes organic molecules that come from food, spinning off carbon dioxide and also hydrogen to be burned with oxygen in respiration. Again going forward, the cycle provides precursors for metabolic biochemical pathways while serving up the hydrogen that’s required to generate ATP. However, spin the cycle in reverse by providing carbon dioxide, hydrogen and ATP and new organic molecules, and the building blocks of life (amino acids/nucleobases) are formed. Strikingly, the reverse spinning of the Krebs cycle is rare in organisms, but common to one particular form of life – Archaea. Nick Lane (4) and others ask, what happens when we begin with carbon dioxide, hydrogen, Krebs cycle molecules and ATP in a geological flow reactor similar to the tubeworm like structures observed by Atlantis?
It’s now easy to wonder; if alkaline vent based, geologically formed, cell-like structures filled up with thermodynamically stable molecules, could it have been long before peptides and RNA arrived? And if that occurred, at what point did LUCA emerge?
Figure 1. Digital maps lifted from Jeff Marshall (1). Map A shows Central America and adjacent sea floor of the Cocos, Nazca, and Caribbean plates. Just 50 km offshore from the Nicoya Peninsula, the Middle America Trench marks where the Cocos Plate subducts beneath the Caribbean Plate. The image also reveals the sea floor formed along the Cocos-Nazca spreading plates that intersects the Middle America Trench offshore of Costa Rica’s Nicoya Peninsula shown in Map B.
Figure 2. A phylogenetic tree of life based on RNA data and proposed by Carl Woese (2). The tree shows the separation of three domains of life, bacteria, archaea, and eukaryotes. Yet, the relationships of the three domains are debated, as is the position of the root of the tree that would represent the last common universal ancestor.
Figure 3. Chitin based remains of what were once marine tubeworm colonies that litter the Playa Ario shoreline in the Nicoya Peninsula.
- Marshall, J. 2009. Megathrust Earthquakes, Coastal Uplift, and Emergent Marine Terraces of Costa Rica’s Nicoya Peninsula, Vignettes: Key Concepts in Geomorphology, http://serc.carleton.edu/vignettes/collection/25559.html
- Woese C, Kandler O, Wheelis M. 1990. Towards a Natural System of Organisms: Proposal for the Domains Archaea, Bacteria and Eucarya, Proc Natl Acad Sci USA 87: 4576–9 http://www.pnas.org/content/87/12/4576.full.pdf+html
- Martin, W, Baross, J, Kelley, D, and Russell, M. 2009. Hydrothermal Vents and the Origin of Life, Nature Reviews Microbiology 6: 805 http://www.nature.com/nrmicro/journal/v6/n11/abs/nrmicro1991.html
- Lane, N. 2010. Why are Cells Powered by Proton Gradients? Nature Education, 3(9):18 http://www.nature.com/scitable/topicpage/why-are-cells-powered-by-proton-gradients-14373960