Biologists are not in complete agreement about exactly where life on Earth first appeared. It could have evolved on the ocean floor, in shallow rock pools, or from building blocks delivered by asteroid impacts — or perhaps all of the above. We know that all life in Earth it needs water to survive, so life likely evolved there. But water alone is not enough to awaken life; it also needs energy.
Today, most living things get their energy from metabolizing sugars, but these molecules did not exist 3.7 billion years ago, when life evolved.
So what energy sources were available to help Earth’s first inhabitants to 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 oceanic world, with occasional volcanic islands poking 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 new tab)a biologist studying 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 said. to Live Science. However, “UV radiation creates a problem of basically breaking anything you have,” Camprubi-Casas said. So even when complex molecules formed, they too would have degraded because of solar radiation.
That’s why Camprubi-Casas and his colleagues suspect that the origin of life occurred somewhere far away from those warm lagoons – at the bottom of the sea, where hot, alkaline water mixed with cold, acidic water, creating a soup of chemical energy that could have provided a spark for the evolution of life.
Deep beneath the ocean’s surface, areas of geothermal activity form at plate boundaries as magma rises from Earth’s mantle. Cold ocean water seeps into the cracks in these hot areas and dissolves the minerals in the rock. When the hot water comes out of the cracks and flows into the cold ocean, the minerals precipitate, forming “chimneys” of organic matter”, explained Camprubi-Casas. This fluid is highly alkaline and contains a lot of hydrogen gas and, during the Hadean, the Earth’s atmosphere was filled with carbon dioxide, much of which dissolved into the ocean, making the ocean slightly acidic.
When the water from the hydrothermal vents combined with the 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 adding nitrogen and oxygen to form the building blocks.” in DNA”, said Camprubi-Casas.
Delivering the building blocks of life from space
One theory of the origin of life on Earth posits that the building blocks of life were delivered by asteroid impacts, which were more common in Hadean than they are today. On an asteroid, a layer of ice would have protected simple sugars and small amino acids – the basic ingredients needed for prebiotic chemistry – from too much strong radiation from the sun, he said. partha bera (opens in new tab)a research scientist at NASA’s Bay Area Environmental Research Institute.
“These bodies are exposed to sunlight for millions of years and produce radicals – active ingredients – that can react with each other 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 hypothesis, 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 start life. In that case, the energy source would also have been geothermal heat, Bera said.
Since there are very few (and small) rock samples from this period in Earth’s history, it is impossible to know exactly which source of energy – the sun, geothermal chemistry or geothermal heat – generated life. evolution. But research in laboratories and many heated debates will help us discover our possible origins.