Follow us on a journey through the theories that try to describe the beginning of life.
The most recent and most precise study aimed at calculating the total number of all species living on Earth estimates there are about 8.7 million species.
It’s estimated that only 1.2 million species are currently described and cataloged by taxonomists. This means that around 86.2% of marine and terrestrial species have yet to be identified.
In the Amazon rainforest alone, a new discovery of animal and plant species is made every other day. In fact, life on Earth is so diverse that scientists identify between 15,000-20,000 new animal and plant species every year!
Even with all the cutting-edge tech like AI and drones now available to scientists in their classification of new species, we may perhaps never know the exact number of all species dwelling on Earth. In fact, many could go extinct before we even catch glimpses of them.
But there’s another longstanding and intriguing question about life on Earth to which we have yet to find a definitive answer: When did Earth see the beginning of life?
When did Life’s “Big Bang” Begin?
In the geological time scale, humans appeared very recently.
Homo sapiens are thought to have appeared some 200,000 years ago. Recently, however, new scientific evidence suggested that humans may be 115,000 years older. This puts the number for the beginning of life for humans at around 315,000 years ago.
However, in the grand scheme of things, that doesn’t change much. If Earth’s existence were to be viewed as a single day, humans would have only appeared in the last 5 minutes.
So much happened on Earth before we came to call it home.
As far as we know, humans are the only sentient beings who can ponder the question of the beginning of life.
We’re eager to know whether humanity is the only technologically-advanced civilization in the universe. But, as a life form, we live in a planet that’s abuzz with living beings even in its most extreme environments.
Over its 4.5 billion years of existence, Earth has hosted an extraordinary variety of living beings. Millions of animal and plant species have appeared and lived before disappearing to give way to other living species to reign.
However, it wasn’t always sunshine and rainbows. During the early stages of Earth’s formation, also known as the Hadean period, Earth’s hellish environment wasn’t conducive to life.
Eventually, the Earth’s primordial soup cooled and gathered the elements and conditions necessary to spark the beginning of life on Earth.
In a similar way to how the Big Bang started the cosmos, early Earth was lifeless. Then, in a short amount of time, (geologically speaking), something kick-started life’s dazzling explosion that we, humans, are part of, and now asking about it.
Liquid water, and life, are thought to have appeared during the Hadean time. This technically is not a geological era per se, as rocks were still forming on our planet.
The age of the Earth has been a bone of contention for millennia. In recent times, the theory for the birthdate of the universe we continuously being pushed back as new discoveries and technological tools came along the way.
From 540 million years in the 1950s, now the old range of life on Earth is between 3.8 and 3.95 billion years. Then again, it could have all been created last Thursday.
Recent discoveries seem to substantiate these estimates. Last December, scientists at UCLA and the University of Wisconsin–Madison confirmed that the microfossils they unearthed in Australia represent the earliest direct evidence of life on Earth.
Found in a 3.5 billion-year-old rock, the fossilized microbial filaments are of biological nature and suggest that life could probably have started even earlier than previously thought.
How did it all Begin? The Secret to the Beginning of Life
If bacterial and microbial lifeforms seem to be the oldest inhabitants of Earth, their origin is perhaps a bigger puzzle.
Many theories have been purported to try to explain the origin of these early unicellular organisms from which more complex life forms have developed.
Now, let’s get down to brass tacks. Here’s a rundown of the most prominent theories of the origin of life, from a historical, philosophical, religious, and scientific perspective
Spontaneous Generation: Life is but a Happy Accident
Aristotle was one of the earliest proponents of the theory of spontaneous generation. He propounded that life can spontaneously arise out of inanimate matter if it contains “vital heat”.
Under the spontaneous generation theory, there are two hypotheses:
Abiogenesis, which is the spontaneous production of biological life from non-living inorganic matter.
Heterogenesis, on the other hand, is the derivation of lifeforms from a different living or dead lifeforms, such as flies from dung or rotten meat.
The spontaneous generation body of the thought is now considered to be obsolete by the scientific community.
The Clay Lattice: Religion and Science Reconciled?
The sacred texts of the three monotheistic religions all evoke the vital role of clay in the process of creation. There are also mentions of clay in religious transcripts of ancient civilizations.
What if religions were true and clay provided a template for organic life to form?
After proposing it in 1966, Scottish chemist Graham Cairns-Smith published in 1985 a hypothesis promoting the role of clay crystals in the development of prebiotic organic molecules.
Smith has spent his career trying to prove that mineral crystals, and not organic structures, are the first source of life.
In a more recent scientific effort (2013), biological engineers at Cornell University report that clay might indeed have been the cradle of organic life.
Using a simulation of ancient water, Cornell researchers found that clay formed a hydrogel that provided a confinement structure for chemical processes to take place until living cells developed their membranes.
There are those who believe in an “Intelligent Design”, which is backed by multiple religions, all of who deny evolution and believe that God created every living being as is, including humans and sent them to Earth.
However, science has yet to find evidence that supports such beliefs. At the moment, to believe it, you have to believe in it.
Panspermia, Cosmic Dust: Life is Originally Extraterrestrial
First formulated in the 1970s, panspermia is a theory suggesting that life didn’t begin on Earth and that the earliest living microorganisms came from space. Usually, these theories postulate that these organisms were carried by asteroids and comets bombarding early Earth.
Some think that it’s on Mars, which comes first in humanity’s roadmap to space colonization, that life on Earth has originated from.
The hypothesis that life isn’t indigenous to Earth and has extraterrestrial origins gained some new traction, with hot streams of cosmic dust proposed as carriers of life’s building blocks.
However, this idea does have its detractors. Some argue that these early living organisms, or seeds of life, hanging on the side of rocks could not survive the harsh trip in interstellar space.
Yet, morning glory seeds have been shown to survive extreme levels of ultraviolet radiation found in outer space. Though that’s by no means direct evidence of life’s extraterrestrial origin, it does give the idea some grounding.
Warm Ponds: Life Began With a big Splash
Some scientists think that RNA molecules should be considered as the earliest life forms, especially due to their self-replicating ability.
A new study provides further support to the theory that meteorites splashing in hot ponds could have delivered the essential ingredients for RNA to form on Earth.
RNA molecules probably arose earlier than 4.17 billion years ago, says the study (published in PNAS), conducted by researchers at McMaster University (Canada) and the Max Planck Institute for Astronomy (Germany).
Was Charles Darwin right? In 1871, Darwin sent a letter to J. D. Hooker, a botanist and a close friend of his, where he claimed that life could have originated from chemical reactions “in some warm little pond.”
A chemical recipe for life has been the subject of research with different approaches from scientists in their effort to formulate it.
In another recent study, chemists at the Scripps Research Institute focused on the chemical reactions within the citric acid cycle (CAC).
Scripps researchers found that the elements necessary for CAC reactions could have been available on early Earth as far back as four billion years ago.
The team also found that the unavailability of some essential ingredients doesn’t prevent the life cycle from taking place. They also identified two non-biological cycles that could have enabled the chemical reactions of the primitive citric acid cycle.