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How Did Life Begin on Earth?

Posted August 26, 2013

No answers today, only a question. But it’s one of the most interesting and meaningful questions we can possibly ask.

Where does life come from? How did we get from no life on Earth, to the rich abundance we see today?

Charles Darwin first published our modern theories of evolution – that all life on Earth is related; adapting and changing over time. Look at any two creatures on Earth and you can trace them back to a common ancestor. Humans and chimpanzees share a common ancestor from at least 7 million years ago.

Trace back far enough, and you’re related to the first mammal who lived 220 million years ago. In fact, you and bacteria can trace a family member who lived billions of years ago. Keep going back, and you reach the oldest evidence of life on Earth, about 3.9 billion years ago.

But that’s as far as evolution can take us.


The Earth has been around for 4.5 billion years, and those early years were completely hostile to life. The early atmosphere was toxic, and a constant asteroid bombardment churned the landscape into a worldwide ocean of molten rock.

As soon as the environment settled down to be relatively habitable, life appeared. Just half a billion years beyond the formation of the Earth.

So how did life make the jump from raw chemicals to the evolutionary process we see today? The term for this mystery is abiogenesis and scientists are working on several theories to explain it.

A simulated ribosome (white and purple subunits) processing an amino acid (green) (credit: Los Alamos National Laboratory)

One of the first clues is amino acids, the building blocks of life. In 1953, Stanley Miller and Harold Urey demonstrated that amino acids could form naturally in the environment of the early Earth. They replicated the atmosphere and chemicals present, and then used electric sparks to simulate lightning strikes.

Amazingly, they found a variety of amino acids in the resulting primordial soup.

Other scientists replicated the experiment, even changing the atmospheric conditions to match other models of the early Earth. Instead of water, methane, ammonia and hydrogen, they wondered what would happen if the atmosphere contained hydrogen sulfide and sulfur dioxide from volcanic eruptions. Environments around volcanic vents at the bottom of the ocean might have been the perfect places to get life started, introducing heavier metals like iron and zinc. Perhaps ultraviolet rays from the younger, more volatile Sun, or abundant radiation from natural uranium deposits played a role in pushing life forward into an evolutionary process.

Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)

Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)

What if life didn’t start on Earth at all? What if the building blocks came from space, drifting through the cosmos for millions of years. Astronomers have discovered amino acids in comets, and even alcohol floating in distant clouds of gas and dust

Maybe it wasn’t the organic chemicals that came first, but the process of self organization. There are examples of inorganic chemicals and metals that can organize themselves under the right conditions. The process of metabolism came first, and then organic chemicals adopted this process.

Thermophilic (heat-loving) bacteria may be among the last living creatures on Earth, the study suggests. Credit:  Mark Amend / NOAA Photo Library

Thermophilic (heat-loving) bacteria may be among the last living creatures on Earth, the study suggests. Credit: Mark Amend / NOAA Photo Library

It’s even possible that life formed multiple times on Earth in different eras. Although all life as we know it is related, there could be a shadow ecosystem of microbial life forms in our soil or oceans which is completely alien to us.

So how did life get here? We just don’t know.

Maybe we’ll discover life on other worlds and that will give us a clue, or maybe scientists will create an experiment that finally replicates the jump from non-life to life.

We may never discover the answer.

Source: Universe Today, story by Fraser Cain

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