When explorers finally make the journey to Titan, they will no doubted search for signs of life. I don’t think anyone is expecting “little green monsters”, but a full-out search for unicellular life will be on the scientific agenda. The most probably source of life will come in the form of prokaryotic organisms, microscopic life that doesn’t have an organized nucleus or most organelles such as mitochondria or chloroplasts. Some of these organisms on Earth can photosynthesize; others are heterotrophs, while some can chemosynthesize. More about those types later, but what does the ancient Earth provide for us as a template to search?
Middle school earth science should have taught us that the Earth is about 4½ billion years old, and in the early stages uninhabitable for life. The surface was hot and molten, and devoid of liquid water. This period known as the Hadean Eon, lasted until about 4 billion years ago. Here comes life…
What is remarkable, is that life seems to appear relatively soon after the cooling of the Earth, and the formation of oceans. Some researchers have speculated that indirect evidence for life may be found in the Eoarchean, which is the period in Earth’s history from 4 – 3.6 billion years ago. At the very least, life was around 3 ½ billion years ago, and the environment for life at this point was quite different from today. Life would evolve under conditions with much lower concentrations of oxygen , and much higher concentrations of methane, which is also found is high levels on Titan.Times, they are a-changin’
What we know from the fossil record and geochemical evidence, is that these early microscopic organisms began to change the Earth’s environment. The main culpit was probably due to photosynthesis. These prokaryotes, just like their eventual descendants the plants, began to split liquid water into hydrogen and oxygen to begin the process of creating sugars for energy. It’s hard to “fossil photosynthesis”, but there is some evidence that the photosynthetic process was happening between 3.4 – 3.0 billion years ago. How do we know about photosynthesis in the fossil record?
Remember the main waste product of photosynthesis is oxygen, and we have indirect evidence that oxygen levels rise quickly after 3 billion years. The Earth’s surface was rich in iron, which is abundant in our Earth’s core and mantle. We have all experienced the result of when oxygen and iron interact; it’s called rust. Around 3 billion years we see amazing banded-iron ore formations
in rocks, as the oxygen (presumably from photosynthesis) reacts with the iron-rich surface. We are all set for an adaptive radiation of life into multicellular and eukaryotic organisms (life with an organized nucleus).What about Titan and life?
Is this the path that Titan took? Could life evolve along this same path? It’s seems difficult to comprehend since the radiant life from the sun and the ambient air temperature are much, much lower and colder, but it would seem that our early Earth is the only template that we have. We will have to extrapolate many things, and I’m sure a microbiologist will be part of the Titan voyage and eager to search for “wee beasties” below the surface and methane lakes of this moon.