Biologists are not entirely in agreement on exactly where the first life on Earth appeared. It may have evolved on the ocean floor, in shallow rock basins, or from building blocks delivered by asteroid impacts – or perhaps all of the above. We know that all life on Earth needs water to survive, so life probably developed there first. But water alone is not enough to trigger life; it also needs energy.
Today, most living beings draw their energy from metabolize sugars, but these molecules did not exist 3.7 billion years ago when life began to evolve.
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 to 4 billion years ago), Earth was largely an ocean world, with occasional volcanic islands rising out of the water. One theory about the origin of life is that ultraviolet (UV) radiation from the sun helped create complex molecules in shallow rock pools on volcanic islands, said Eloi Camprubi-Casas (opens in a new tab)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 it generates ionized molecules, making them more reactive” and more likely to combine into the larger, more complex molecules needed to generate the building blocks of life, a Camprubi-Casas told Live Science. . However, “UV radiation generates a problem of decomposing everything you have,” Camprubi-Casas also said. So even as complex molecules formed, they would also have degraded due to solar radiation.
This is why Camprubi-Casas and his colleagues suspect that the origin of life took place somewhere far from these warm ponds – at the bottom of the sea, where warm, alkaline water mixed with cold and acidic, creating a soup of chemical energy that could have provided a spark for the evolution of life.
Deep below the ocean surface, areas of geothermal activity form at plate boundaries as magma rises from the Earth’s mantle. Cold ocean water seeps through cracks in these warm areas and dissolves the minerals in the rock. As hot water exits cracks and flows into the cold ocean, minerals rush in, forming ‘chimneys’ of organic matter,” Camprubi-Casas explained. This fluid is highly alkaline and contains a lot of hydrogen. gaseous, and during the Hadean, the earth’s atmosphere was exploding with carbon carbon dioxide, much of which dissolved into the ocean, making the ocean slightly acidic.
When the water from the hydrothermal vents combined with carbon dioxide dissolved in the water, the resulting molecules became “much more chemically active, and you can start adding nitrogen to make amino acids or add nitrogen and oxygen to form the building blocks of DNA“, said Camprubi-Casas.
Delivering the Basics of Life from Space
A theory about the origin of life on Earth posits that the building blocks of life were provided by asteroid impacts, which were more frequent in the Hadean than they are today. On an asteroid, a layer of ice would have shielded simple sugars and small amino acids — the raw ingredients needed for prebiotic chemistry — from much of the sun’s harsh radiation, said Partha Bera (opens in a new tab)researcher at NASA’s Bay Area Environmental Research Institute.
“These bodies are exposed to sunlight for millions of years, and they produce radicals – active ingredients – that can react with each other even at low temperatures,” Bera told Live Science. The radicals are atomsmolecules or ions with an extra electron, making them ready to react with anything.
According to this origin of life assumption, when these asteroids hit 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 would also have been geothermal heat, Bera said.
Because there are very few (and small) rock samples from this period of Earth’s history, it is impossible to know exactly which source of energy – the sun, geothermal chemistry or geothermal heat – has triggered life. evolution. But laboratory research and much heated debate will help us determine our possible origins.