The first research article focuses on the collapse of life on Earth after the Great Oxidation Event (GOE), a dramatic growth of atmospheric oxygen some 2.5 billion years ago that was followed by an extinction event. Described as an “oxygen overshoot” Earth’s microbial plant life flourished producing copious levels of oxygen. Paleobiologists describe the GOE and the following transition as a period of feast and famine that lasted 1 billion years.
The clues are found in multi-billion year-old rocks on an island at the north end of Hudson Bay in Canada’s Arctic. The mineral barite laid down at the time captured the oxygen levels in the atmosphere showing huge changes as a result of the planet’s growing biosphere, followed by a massive drop off of life around 2 billion years.
The GOE happened because of the blooming of life in Earth’s early oceans. Ancient microbial plants (think algae) through photosynthesis flooded the atmosphere with oxygen. The growth was spectacular producing lots of free oxygen absorbed into the atmosphere. When food supplies ran out, like an algae bloom that grows and dies, the microbial population collapsed as did the amount of oxygen in the atmosphere.
It was far different than today where plants and animals balance each other out keeping oxygen levels in the atmosphere in equilibrium. Early earth was anything but stable for life to establish itself. And it tells us something about our Earth today and the fine balance that keeps our planet in equilibrium.
The recent fires in the Arctic and Amazonia, we are told, could alter the balance of atmospheric gases, as well as cause significant harm to Earth ecosystems dependent on the forests in these areas. It tells us about how positive feedbacks from changes to planetary conditions can produce catastrophic outcomes.
In the ancient atmosphere, the successful expansion of microbial plant life created a super oxygenation event which reinforced life’s growth beyond the carrying capacity of the planet’s environment at that time. In the end it led to a series of extinction events. In our modern discussions about climate change, we refer to such events as tipping points.
The second story that caught my eye was about a earlier in the year announced discovery in Alaska where researchers drilling into the permafrost found a trapped briny water deposit called a cryopeg. The scientists estimated the water had been preserved under a permafrost cap for 50,000 years.
This wasn’t ordinary water. In its isolated environment, it was filled with concentrated salt (14% by weight) and ti was very cold. Water this salty, if used to preserve canned foods would be sufficient to kill any bacteria on the surface of the planet today. So could anything survive in this ancient pocket of saltwater?
Described as a robust community of microbes and viruses, the scientists were startled by not only the existence of, but also the density of this living community. In fact, the amount of life found in the cryopeg appeared to be in concentrations much greater than would we bound under sea ice today anywhere on our planet.
For exobiologists studying ice deposits on Mars, and the planets and moons from the Outer Solar System, the discovery strongly suggests, that life once established, has an ability to flourish even in the most extreme and exotic environments.
The implications for life on Mars which was once home to a surface ocean and today contains subsurface ice deposits, could be enormous. Or for life on Europa, Jupiter’s sixth-closest moon, characterized by a thick icy crust concealing a saltwater ocean with water volumer larger than all the oceans on Earth. Or for Saturn’s moons, Enceladus and Titan, both with saltwater oceans of their own lying beneath the surface. Or for Triton, Neptune’s largest moon, which could also harbour life in its watery depths. And finally, for Pluto, the dwarf planet of the Kuiper Belt that also, as we have recently learned, is geologically active, and is suspected of having its own subsurface ocean.
If life can be found deep under the surface of Earth where none was anticipated, and if that life can survive for tens of thousands to millions of years without access to the surface, then conceivably life can exist in these other extreme environments. That once life establishes itself for even a short period of time it can become robust enough to survive changes to its environment that we would consider extreme, and yet thrive.
That is one of the reasons for concerns about NASA’s ambitions to land human explorers on Mars in the 2030s, or Elon Musk’s call to establish a human settlement on the Red Planet by the mid-century. If we are to go to Mars carrying our own microbiome, we may permanently alter the native life of Mars as we probe into its ancient subsurface ice formations in pursuit of resources we will need to survive there: hydrogen, oxygen, and water.
And NASA has also announced a Europa mission in the works to first survey the moon from orbit, and possibly even deploy a lander to look for what lies beneath its icy surface. The fear is we are as likely to plant life there from Earth as we are to find Europan native life. To me, that is a disturbing consequence of our current scientific and human space mission planning.
]]>Spirit, the first of two Martian rovers which finally died when it got stuck in sand, found outcrops of nodular silica distributed across basaltic bedrock that resembles volcanic hydrothermal signatures here on Earth. On our planet we see this type of rock signature near no longer active hot springs and geysers. Such is the case in El Tatio, Chile.
When Spirit first rolled over the Gusev Crater site it used its thermal emission spectrometer to identify the silica in the rocks. The results from Gusev show qualitative similarities to the nodules at El Tatio. Seen below, El Tatio features hot springs, stone barricades and silica deposits in the middle of volcanic basalt deposits.
The next picture shows a comparison between opaline silica structures found at Gusev Crater with side-by-side images from El Tatio. The resemblance is uncanny. At El Tatio, the micro-environmental conditions created by microbial biofilm and mat communities thriving in water at temperatures greater than 40 Celsius (104 Fahrenheit) creates the shapes and nodular structures seen on the right. The images from Mars at similar scale appear nearly identical. Some of the rocks examined by Spirit appear to have similar porosity to what is seen at El Tatio to have been shaped by biology as well as by aeolian abrasion (wind).
Spirit arrived on Mars in January 2004, several weeks before its twin rover Opportunity. Spirit was the first to encounter opaline silica as it traced a route through Gusev Crater. Gusev Crater and El Tatio have some similar physical characteristics. El Tatio is located in a particular arid part of Chile and at a high elevation. The low precipitation rate, high evaporation, and extremes of heat and cold plus high ultraviolet irradiance makes it as close to a Martian landscape as any place on Earth.
The two authors of the paper, Steven Ruff and Jack Farmer, both at the School of Earth and Space Exploration, Arizona State University, write “Because we can neither prove nor disprove a biological origin for the microstromatolite-like digitate silica structures….they constitute a potential biosignature according to this definition.”
Spirit got stuck in soft Martian sand in May 2009 and finally died in May 2011. Opportunity is still chugging away 12 years after arriving on Mars and is now on the rim of Endeavour Crater. It too has discovered evidence of water on the surface of Mars having identified outcrops of calcium sulfate and gypsum at a place name Whitewater Lake. Curiosity, the next generation rover that joined its two predecessors, literally landed on a dried out river bed in Gale Crater.
The next rover to come to Mars, currently in planning for 2020, may provide a more definitive answer to the possible biological origin of the silica structures Spirit first identified. That successor to Curiosity will have the capability of obtaining and storing samples that can be returned to laboratories here on Earth to allow us to reach a definitive conclusion.
]]>