Life on Earth may have been kickstarted by a stormy and active sun

New research suggests that the first building blocks of life on Earth may have been formed due to solar eruptions from the Sun. 

The study, published in the journal Life, presents a series of chemical experiments that demonstrate how solar particles, upon colliding with gases in Earth’s early atmosphere, can give rise to amino acids and carboxylic acids. These organic compounds serve as the basic building blocks of proteins and life as we know it.

The origins of life have long been a topic of fascination and debate among scientists. One of the most well-known theories dates back to the late 1800s, proposing that life may have begun in a “warm little pond.” 

This primordial soup of chemicals would have been energized by various sources such as lightning, heat, and other forms of energy. These elements would then combine in concentrated amounts, leading to the formation of organic molecules.

Creating primordial soup in the lab

In an attempt to recreate these primordial conditions, Stanley Miller, a scientist at the University of Chicago, conducted a groundbreaking experiment in 1953. 

Miller filled a closed chamber with methane, ammonia, water, and molecular hydrogen – gases believed to have been prevalent in Earth’s early atmosphere. He then introduced an electrical spark to simulate lightning. 

After a week, Miller and his graduate advisor, Harold Urey, analyzed the contents of the chamber and discovered the formation of 20 different amino acids.

Vladimir Airapetian, a stellar astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and coauthor of the new study, said, “That was a big revelation. From the basic components of early Earth’s atmosphere, you can synthesize these complex organic molecules.”

However, the understanding of Earth’s early atmosphere has evolved over the past 70 years, complicating this interpretation. Ammonia (NH3) and methane (CH4) are now thought to have been far less abundant. 

Instead, Earth’s air was likely filled with carbon dioxide (CO2) and molecular nitrogen (N2), which require more energy to break down. These gases can still yield amino acids but in significantly reduced quantities.

This realization has led scientists to seek alternative energy sources for the synthesis of amino acids. Some have suggested that shockwaves from incoming meteors could have provided the necessary energy, while others have cited solar ultraviolet radiation. 

Inspired by the Kepler mission

Airapatian, drawing on data from NASA’s Kepler mission, has introduced a new possibility: energetic particles from our Sun.

Kepler, designed to observe far-off stars at various stages of their lifecycle, has offered clues about our Sun’s past activity. In 2016, Vladimir Airapetian published a study suggesting that during Earth’s first 100 million years, the Sun was approximately 30% dimmer. 

However, powerful eruptions known as solar “superflares” would have occurred once every 3-10 days, as opposed to the once every 100 years or so we observe today. These superflares launch near-light speed particles that would frequently collide with Earth’s atmosphere, initiating chemical reactions.

Airapetian explained, “As soon as I published that paper, the team from the Yokohama National University from Japan contacted me.” 

Dr. Kobayashi, a professor of chemistry at the university, had spent three decades studying prebiotic chemistry. He was investigating how galactic cosmic rays, incoming particles from outside our solar system, could have impacted early Earth’s atmosphere. 

Kobayashi stated, “Most investigators ignore galactic cosmic rays because they require specialized equipment, like particle accelerators. I was fortunate enough to have access to several of them near our facilities.” Minor adjustments to Kobayashi’s experimental setup could put Airapatian’s ideas to the test.

How this study was done

Together, Airapetian, Kobayashi, and their colleagues created a mixture of gases that mirrored early Earth’s atmosphere based on current understanding. They combined carbon dioxide, molecular nitrogen, water, and a variable amount of methane (the methane proportion in Earth’s early atmosphere is uncertain but believed to be low). 

The team exposed the gas mixtures to protons (simulating solar particles) or ignited them with spark discharges (simulating lightning) to replicate the iconic Miller-Urey experiment for comparison purposes.

The researchers found that when the methane proportion was over 0.5 percent, the mixtures exposed to protons (solar particles) produced detectable amounts of amino acids and carboxylic acids. However, the spark discharges (lightning) required a methane concentration of around 15 percent before any amino acids formed at all. 

Airapetian added, “And even at 15 percent methane, the production rate of the amino acids by lightning is a million times less than by protons.” Protons also tended to yield more carboxylic acids (a precursor of amino acids) than those ignited by spark discharges.

What the researchers learned

Considering all factors, solar particles appear to be a more efficient energy source for creating life’s building blocks than lightning. However, Airapetian suggested that the conditions were likely not equal. 

Miller and Urey assumed that lightning was as common during the “warm little pond” era as it is today. Nevertheless, lightning, which originates from thunderclouds created by rising warm air, would have been less frequent under a 30 percent dimmer Sun.

“During cold conditions you never have lightning, and early Earth was under a pretty faint Sun. That’s not saying that it couldn’t have come from lightning, but lightning seems less likely now, and solar particles seem more likely,” said Airapetian.

The study opens up new avenues for understanding the origins of life on Earth and highlights the potential role of solar activity in the formation of life’s basic building blocks. As researchers continue to explore these theories and conduct further experiments, we may come closer to unraveling the mysteries of life’s beginnings.

More about the conditions on early Earth

Early Earth refers to the period of Earth’s history from its formation around 4.6 billion years ago to the emergence of the first life forms approximately 3.5 to 4 billion years ago. This period is characterized by significant geological, atmospheric, and environmental changes that ultimately set the stage for the development of life on our planet. Some key aspects of early Earth include:

Formation

Earth formed through the process of accretion, where dust and debris in the protoplanetary disk surrounding the young Sun gradually clumped together to form larger bodies, ultimately creating our planet. This process took around 10-20 million years.

Hadean Eon

The first geological eon in Earth’s history, the Hadean Eon, lasted from about 4.6 to 4 billion years ago. During this time, the planet’s surface was a molten mass with temperatures reaching up to 2,000 degrees Celsius (3,632 degrees Fahrenheit). As the Earth gradually cooled, a solid crust began to form.

Formation of the Moon

It is widely believed that the Moon was formed about 4.5 billion years ago when a Mars-sized body called Theia collided with the young Earth. The debris from this collision eventually coalesced to form the Moon.

Atmosphere

Early Earth’s atmosphere was vastly different from what we know today. It primarily consisted of gases like hydrogen, helium, water vapor, methane, and ammonia. Over time, volcanic activity and other processes contributed to the increase of carbon dioxide, molecular nitrogen, and water vapor in the atmosphere. The oxygen we breathe today did not become significant until photosynthesizing organisms, such as cyanobacteria, emerged and started releasing oxygen through the process of photosynthesis.

Oceans

As the Earth cooled, water vapor in the atmosphere condensed, and along with water from volcanic activity and icy comets, eventually formed the first oceans around 4.3 billion years ago.

Emergence of life

The first evidence of life on Earth dates back to around 3.5 to 4 billion years ago. These early life forms were simple, single-celled organisms, such as bacteria and archaea. The exact origin of life is still a subject of ongoing research and debate, with various theories suggesting that life may have originated in deep-sea hydrothermal vents, shallow ponds, or even from outer space through panspermia.

Geological activity

The early Earth experienced intense geological activity, including volcanism and tectonic movements. These processes played a crucial role in shaping the planet’s landscape and atmosphere, providing the necessary conditions for life to emerge and evolve.

Throughout its early history, Earth underwent dramatic transformations that ultimately led to the diverse, life-supporting planet we know today. Understanding early Earth helps scientists gain insights into the processes that allowed life to form and flourish and informs the search for life beyond our planet.

Other theories for the evolution of life on Earth

In addition to the widely-accepted theories about the origins of life on Earth, there are several alternative hypotheses that have been proposed by scientists. These theories seek to explain how life might have evolved from simple organic molecules to the complex organisms we see today. Some of the alternative theories include:

Panspermia

This hypothesis suggests that life on Earth originated from extraterrestrial sources, such as comets or meteorites, which delivered organic molecules to our planet. These molecules then provided the building blocks for the formation of life. Some variations of this theory propose that simple life forms, like bacteria or viruses, were transported to Earth via space debris.

Clay hypothesis

Proposed by A. G. Cairns-Smith, this theory posits that the first life forms on Earth originated on clay minerals. Clay minerals have the ability to catalyze chemical reactions, which could have facilitated the formation of organic molecules. Over time, these organic molecules formed more complex structures, eventually giving rise to life.

Deep-sea hydrothermal vents

According to this hypothesis, life on Earth began near deep-sea hydrothermal vents, which are fissures in the Earth’s crust that release geothermally heated water. The chemical reactions occurring in these high-pressure, high-temperature environments could have provided the necessary energy and conditions for the formation of the first organic molecules and, eventually, the first life forms.

Autocatalytic sets

Proposed by Stuart Kauffman, this theory suggests that life originated from a collection of molecules that were capable of self-organization and self-replication. These molecules formed a self-sustaining network of chemical reactions, which eventually led to the emergence of simple living organisms.

RNA World hypothesis

This widely-supported theory posits that the first life forms were based on ribonucleic acid (RNA) rather than deoxyribonucleic acid (DNA). RNA molecules have the ability to store genetic information and catalyze chemical reactions, making them ideal candidates for the first self-replicating molecules. Over time, RNA-based life forms evolved into more complex organisms, incorporating DNA and proteins into their molecular machinery.

Virus-first hypothesis

This theory proposes that viruses were the first life forms on Earth. Viruses are simpler than cells, and proponents of this hypothesis argue that they could have evolved from self-replicating molecules in the early Earth’s environment. Eventually, these early viruses would have infected and integrated with more complex cellular life, leading to the development of modern organisms.

These alternative theories provide a range of potential explanations for the origins and early evolution of life on Earth. While some of these hypotheses have gained more traction than others, they all contribute to our understanding of the complex processes that gave rise to the diverse array of life we see today.

Image Credit: NASA

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