Even Futurists Look To The Past In The Search For Life Elsewhere In The Universe

I consider that since I began writing this science and technology blog for the past fourteen years where I have focused on our technological and scientific progress in the 21st century, I have become a bit of a futurist. That’s far from what I was in university where I studied Roman history, the rise of Islam and the Middle Ages. In addition, I spent a considerable amount of time looking at religion, origins, syncretism commonalities and creation myths.

All religions try to explain away the things and events we try to contemplate through our five senses. To address the unknown religions offer us gods with supernatural powers. The commonalities in creation myths tell stories of the beginning of Earth and us that are far different from what scientific research and the geological record show.

The story science tells is far more intriguing than the words in Genesis or any other creationist text. Science tells us that our planet’s beginnings started more than 4.5 billion years ago. Then the Earth was a lumpy and growing protoplanet acquiring mass from numerous collisions with other bodies orbiting the young Sun. In time the mass became great enough for gravity to turn it into a spherical body. Every strike contributed to the planet’s spin and some likely caused the planet’s axis to tilt to where it lies today at a near 23.5-degree cant.

The material the early Earth collected from the Solar System included metals, carbon, water and gasses. Heavy elements like iron migrated from the surface sinking to the planet’s core. Iron has ferromagnetic properties. As the core and planet grew the interior heated up. A band of molten iron circled the solid core and its movement generated by the planet’s spin produced Earth’s protective magnetic field. Venus and Mars did not experience the same geological progress and hence the two sister planets don’t have a magnetic field as robust as Earth’s.

A spinning Earth created conditions for life to emerge. The axial tilt made seasons possible. The daily rhythm of the planet and seasonal variation influenced temperature, precipitation, and other critical environmental factors. These key characteristics played an important role in the emergence of life.

How Life Got  Started

Scientists study the age and chemistry within the rocks that form Earth’s crust to piece together a picture of what the early Earth was like. It bears little resemblance to our world today where the atmosphere contains abundant amounts of oxygen. Earth’s early atmosphere was mostly carbon dioxide (CO2) with other gasses like methane (CH4) and water vapour (H2O) present.

Mars and Venus today both have atmospheres largely made up of CO2. Venus’s atmosphere is dense. Mars’s atmosphere is tenuous. Early Earth’s atmosphere was somewhere in between these two. The common ingredient in all three was the presence of carbon and it is the molecule that interacted with early Earth’s other chemistry to produce complex molecular compounds eventually leading to amino acids and double-helix, self-replicating DNA.

Whether life came from elsewhere in the Solar System, or spontaneously emerged remains a continuing debate. But rocks on Earth that date back 3.7 billion years are the first that we have found to contain fossilized remnants of microbes. These single-celled microbes formed sticky mats bound together by sand and secretions. In death, the mats mineralized to form hard, layered structures called stromatolites. Living stromatolite mats can be found on Earth today containing microbes. The microbes 3.7 billion years ago were anaerobic, that is, they thrived in an oxygen-free world. Anaerobic organisms are still with us today and can be found in the most hostile environments including our gut.

Life on Earth didn’t change much for the next 2 billion years as the Solar System settled into the pattern we see today, four small rocky planets circling close to the Sun, and four icy giant planets further out all in some form of harmonious synchronicity.

In Earth’s early history, the planet went through violent cataclysms as its crust fractured into plates that began drifting across the surface. The dynamic forces causing the planet’s physical changes made it a challenge for living things to thrive. Disruptions from cataclysmic events led to numerous extinctions and rebirths over 2 billion years. But at some point, relative stability ensued and the environment led to the emergence of cyanobacteria (see image below). This happened between 2.7 and 2.4 billion years ago.

Cyanobacteria may be a term unfamiliar to you. Blue-green algae is a cyanobacteria. What characterizes this form of life is its ability to harvest energy from sunlight which in combination with water produces sugars to support cellular metabolic processes.

When did cyanobacteria get this ability? A paper published this month in Nature describes evidence of photosynthesis in cyanobacteria fossils found in 1.73 to 1.78 billion-year-old rocks. These fossil bacteria exhibit structures called thylakoid membranes. Thylakoid membranes are where photosynthesis takes place. Before this discovery, the earliest known cyanobacteria fossils containing thylakoid membranes dated back 500 million years.

What’s the deal with thylakoids? They are found in chloroplasts, the specialized cells found in plants where photosynthesis occurs. A thylakoid membrane contains chlorophyll to capture solar energy and in the presence of water and CO2 convert it into sugar and oxygen.

Without cyanobacteria and thylakoids, the world would not have experienced the Great Oxidation Event when oxygen levels in the atmosphere and ocean began to rise. The event is marked by oxidated chemicals found in rocks laid down as sediments on ocean floors dating back well over a billion years. The paper describes the finding of thylakoid membranes in Australian fossils between 1.73 and 1.78 billion years old and in fossils in Canada between 900 million and 1.01 billion years old.

What was the Earth like at the time of the oxidation event? Imagine the world’s oceans covered by mats of blue-green algae blooms. Their life cycle and decomposition would have produced the same results seen in algae blooms today that cause life and death cycles as their decomposition robs the water of oxygen. The cycles of life and death back then would have made it difficult for new life forms to emerge.

Relating the Past to the Future

In the 21st century, we have turned to neighbouring planets and the stars in the search for life elsewhere. Will its origin stories be the same as ours? Are the rovers on Mars equipped with tools to detect any kind of life or only life as we know it? The James Webb Telescope is powerful enough to sniff the atmosphere of exoplanets. Will the detection of oxygen and other life-friendly gasses on planets light-years away answer the question scientists have continued to ask, “Are we alone in the Universe?”

By understanding how life came to be here, we are not limited to the Earth in the present to make the call on the existence of life elsewhere or not. Earth had life 3.7 billion years ago in conditions we would never consider as amenable to its existence. Earth through time has witnessed dramatic changes to the life upon it. When we look beyond Earth for the conditions that could produce life elsewhere, our search criteria have broadened considerably by studying the planet’s past.