The origins of life present some of the most thought provoking questions of modern science. Our knowledge of the birth and evolution of cells, from which all current forms of life are built (bacteria and humans alike), is shrouded by the mystery of the conditions on Earth four billion years ago. Why and how did cells first appear? Was this inevitable, or a total fluke? Might this happen elsewhere in the universe?
A group of researchers at University College London have been tackling these very questions. Their story began with an exploration of the birth of the first cells on Earth and will soon be accelerated to the furthest reaches of the Milky Way by an innovative new space telescope. The combined results could prove ground-breaking for our understanding of the evolution of life on Earth, and our search for life in the Milky Way.
THE 'SHOPPING LIST FOR LIFE'
The University College London team, led by Dr Nick Lane of the department of Genetics, Evolution and Environment, has suggested that four billion years ago systems of hydrothermal vents on the bed of the Earth’s global ocean could have been the cradles of life. Each vent is a “labyrinth of interconnected pores” says Dr Lane, permeated by hydrothermal fluids. By recreating the deep-sea systems in the lab the team showed that the vents act as continuous electrochemical reactors where hydrothermal fluids, which are abundant in hydrogen, react with the surrounding carbon dioxide-rich ocean water. When these inorganic chemicals react they form simple organic molecules, the chemical building blocks of life.
The work of the hydrothermal vents doesn’t stop there. Convection currents within the porous systems drive the simple organic molecules to the high concentration levels we find within cells. When highly concentrated the organics begin to interact to form more complex molecules such as ribose and deoxyribose, fundamental components of RNA and DNA respectively. Finally, cell-like structure can evolve. As Dr Lane explains, “If you are producing things at high enough concentration they spontaneously form structures which are cell-like in their properties”.
This simple evolutionary tale, from hydrogen and carbon dioxide to cell-like structures, is facilitated entirely by hydrothermal vents and provides clues to the origins of life not just on Earth but on other planets in the Milky Way. Hydrothermal vents are formed in a simple chemical reaction between water and olivine, an iron-rich rocky material ubiquitous throughout the universe, and are therefore likely to be found on any wet, rocky planet. Dr Lane explains, “the kind of conditions required for life, what I like to call the shopping list for life, which is basically rock, water and carbon dioxide, could be found on millions or billions of exoplanets, so life should be everywhere in the form of bacteria”.
SEARCHING FOR LIFE IN THE MILKY WAY
Given the length of the ‘shopping list’, the odds of finding life in the Universe seem better than ever and, in perfect timing, the search is set to be fast-tracked by the work of Twinkle, the first space satellite dedicated to the exploration of the atmospheres of exoplanets. To date, almost 2000 exoplanets have been discovered but little is known about their characteristics. As Katy Chubb of the ExoMol group at University College London explains, “we’ve been discovering all of these planets but now the next stage is to work out what’s in their atmospheres, what they’re made out of and what the conditions are like on them”.
Twinkle is set to be launched into a low-Earth orbit within three to four years by a collaborative UK team from University College London and Surrey Satellite Technology. The small, low-cost satellite will use spectroscopy, the study of light, to determine the conditions on at least 100 exoplanets. When an exoplanet passes in front of the star it orbits, a small percentage of the star’s light passes through the atmosphere of the planet. Observations of this light enable scientists to build up a spectral ‘fingerprint’ which can reveal the chemical composition, temperature and even weather conditions present on the orbiting planet. Combined with the work of Dr Lane and his team, the results of this revolutionary space satellite will allow scientists to identify planets with conditions that might have once harboured life or have the potential to in the future.
This research was presented as part of an exhibit at the Royal Society Summer Science Exhibition held from 30 June to 5 July 2015.