What energy source sparked the evolution of life?
Leading theories suggest that the first energy used by life was either from the sun or from geothermal heat and chemistry at the bottom of the ocean.
Biologists aren't in full agreement about exactly where the first life on Earth appeared. It might have evolved at the bottom of the ocean, in shallow rock pools or from building blocks delivered by asteroid impacts — or maybe all of the above. We do know that all life on Earth needs water to survive, so life likely first evolved there. But water alone isn't enough to spark life; it also needs energy.
Today, most living things get their energy from metabolizing sugars, but those molecules didn't exist 3.7 billion years ago, when life first evolved.
So what energy sources were available to help Earth's first inhabitants appear?
Related: What makes Earth so perfect for life?
During the Hadean eon (about 4.6 billion to 4 billion years ago), Earth was largely an ocean world, with the occasional volcanic island poking out of the water. One theory about the origin of life is that ultraviolet (UV) radiation from the sun helped to create complex molecules in shallow rock pools on volcanic islands, said Eloi Camprubi-Casas, a biologist who studies the origin of life at The University of Texas Rio Grande Valley.
"UV [radiation] is great because it's so energetic that it will generate ionized molecules, making them more reactive" and more likely to combine into the larger, more complex molecules needed to generate the building blocks for life, Camprubi-Casas told Live Science. However, "UV radiation generates a problem of basically breaking down anything you have," as well, Camprubi-Casas said. So, even as complex molecules formed, they also would have degraded because of the sun's radiation.
That's why Camprubi-Casas and his colleagues suspect that the origin of life took place somewhere far away from those warm ponds — at the bottom of the sea, where hot, alkaline water mixed with cool, acidic water, creating a soup of chemical energy that could have provided a spark for life's evolution.
Deep below the ocean's surface, areas of geothermal activity form at plate boundaries as magma rises from Earth's mantle. Cold ocean water seeps into cracks in these hot areas and dissolves minerals from the rock. When the hot water rises out of the cracks and flows into the cold ocean, the minerals precipitate out, forming "chimneys' of organic material," Camprubi-Casas explained. That fluid is highly alkaline and contains a lot of hydrogen gas, and during the Hadean, Earth's atmosphere was bursting with carbon dioxide, much of which dissolved into the ocean, making the ocean slightly acidic.
When water from the hydrothermal vents combined with carbon dioxide dissolved in water, the resulting molecules became "much more chemically active, and you can start adding nitrogen to make amino acids or adding nitrogen and oxygen to form the building blocks of DNA," Camprubi-Casas said.
Delivering life's building blocks from space
One theory about the origin of life on Earth posits that life's building blocks were delivered by asteroid impacts, which were more common in the Hadean than they are today. On an asteroid, a layer of ice would have protected simple sugars and small aminos acids — the raw ingredients needed for prebiotic chemistry — from a lot of the sun's harsh radiation, said Partha Bera, a research scientist at NASA's Bay Area Environmental Research Institute.
"These bodies get exposed to sunlight for millions of years, and they produce radicals — active ingredients — that can react with each other even at low temperature," Bera told Live Science. Radicals are atoms, molecules or ions with an extra electron, making them ready to react with anything.
According to this life-origin hypothesis, when those asteroids struck Earth, the highly reactive molecules would have mixed with other simple molecules in the ocean to create the complex chemistry needed to jump-start life. In this case, the energy source also would have been geothermal heat, Bera said.
Because very few (and small) rock samples exist from this period in Earth's history, it's impossible to know exactly which energy source — the sun, geothermal chemistry or geothermal heat — sparked life's evolution. But research in labs, and a lot of spirited debate, will help us sort out our possible origins.
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JoAnna Wendel is a freelance science writer living in Portland, Oregon. She mainly covers Earth and planetary science but also loves the ocean, invertebrates, lichen and moss. JoAnna's work has appeared in Eos, Smithsonian Magazine, Knowable Magazine, Popular Science and more. JoAnna is also a science cartoonist and has published comics with Gizmodo, NASA, Science News for Students and more. She graduated from the University of Oregon with a degree in general sciences because she couldn't decide on her favorite area of science. In her spare time, JoAnna likes to hike, read, paint, do crossword puzzles and hang out with her cat, Pancake.
By Briley Lewis
By Harry Baker
Evolution is NOT about how life began, it is about how life develops and changes, generation over generation, and from that EVOLVES!
How abiogenesis developed is still a complete unknown with many competing hypotheses and MUCH speculation. How life continues on into various forms "most wonderful" is well understood.
When people who do not understand evolution or the concept of abiogenesis read articles such as this, they conflate (as YOU have!) the two concepts. This very much clouds the understanding of both of them.
No, oxygen is not required (nor was it present for the next billion years after Earth's formation) for life's emergence; there is indeed a consensus on this. No one uses O2 in their prebiotic chemistry experiments.
On the topic of the 'water problem', there's now dozens of great papers showing polymerization under wet conditions without using wet-dry cycling. This is achieved by chemical activation of the monomers, which is exactly how cells polymerize monomers btw.
Darwinian evolution needs mainly two things: (1) natural selection acting upon variance and (2) a sufficiently good heredity mechanism so that information is carried over vertically through generations. There's plenty of competent Origins scientists who think evolution can happen in chemical systems which we wouldn't yet call alive. Chances are gene-based Darwinian evolution is only a subset of all possible evolutionary types. So this 'conflation' you talk about is very much an active discussion point amongst experts.
relative to gravity or down may offer an explanation for most everything. Seems someone else thought the same thing.
Wrong again. Evidence shows anoxygenic photosynthesis (photosynthesis that doesn't generate O2) preceded oxygenic photosynthesis. Here, read a bit: https://doi.org/10.1016/B978-0-08-047514-1.50013-5. There's plenty of stromatolites (colonies of photosynthetic organisms doing non-oxygenic photosynthesis) found in the Archaean eon before we see evidence of oxygen accumulating in the atmosphere.
Peptide and nucleotide bonds have shown to form non-enzymatically under aqueous conditions. This is exactly what our cells do (chemical activation of the monomers), so of course it's possible LOL. Here, free education for you: https://link.springer.com/article/10.1007/BF01732030.