[OPINION] The paradox of the faint young sun, the origin of life, and the modern cell

The following is the 37th in a series of excerpts from Kelvin Rodolfo’s ongoing book project “Tilting at the Monster of Morong: Forays Against the Bataan Nuclear Power Plant and Global Nuclear Energy.“

In the beginning

The conventional wisdom about Earth’s life is like Baby Bear’s porridge in Goldilocks and the Three Bears: unlike Venus, too close to the Sun and too hot, or Mars, too far and too cold, Earth’s temperature was just right. It was a well-lit, well-watered garden just waiting for seeds.

Not true! The “Gaian” perspective: life began despite horrendously difficult conditions, and has shaped and maintained the environment ever since.

The paradox of the faint young sun

The Sun came into being 4.6 billion years ago, a gigantic dust cloud in space that collapsed on itself for about 30 million years before igniting into a mature star.

But it still was only 70% as luminous as it is now, and has been heating up ever since.

Paradox: the new Sun was so cool all Earth’s water should have been frozen. An icy, white planet would reflect off so much sunlight it would remain frozen.

But it isn’t, and rocks 3.8 billion years old were deposited in water!

The answer? Young Earth’s vigorous volcanism was belching out much gas. The atmosphere contained methane and 3% carbon dioxide, a hundred times more than today’s 0.03%. A strong Greenhouse Effect compensated for the weaker Sun, keeping Earth warm enough for liquid oceans.

But volcanoes continued spewing out CO₂, and the Sun kept warming up. Why didn’t the oceans boil off?

Answer: living things emerged and moderated the Greenhouse Effect by removing CO₂from the air and ocean. How? By combining it with calcium dissolved in the oceans to make calcium carbonate for their shells, which slowly accumulated as limestone. And some of their tissues were slowly buried underground as oil, methane, and later, coal.

Gaia had taken over, and has molded and maintained the living planet ever since.

Lifeless, Venus continues to accumulate its massive CO₂ atmosphere. Its volcanism sweats out water molecules, the runaway Greenhouse heat rips them apart into hydrogen that escapes into space, and oxygen that forms solid rust and rock.

How life made and keeps Earth livable

Although newborn Earth wasn’t frozen over, it was too deadly for life. Atmospheric oxygen would come much later. Ozone molecules are three oxygen atoms bonded together; no oxygen, no ozone in Earth’s atmosphere to intercept the Sun’s X-rays and ultraviolet waves fiercely irradiating Earth’s surface.

How life began remains unclear. A likely place would be under enough ocean water to filter out the X- and ultraviolet rays. Perhaps at underwater volcanoes, energetic places with complicated chemistries. The first living stuffs may have organized themselves on the microscopic crystal structures of clay minerals.

Crude living forms arose about 3.5 billion years ago. No larger than 1- millionths of a meter (microns), these cells are called “procaryotes” – “before kernels” or “before nuclei” – because they came long before the much more sophisticated “eucaryote,” “good nuclei” cells of more advanced life, including ours.

Every procaryote has a sloppy “nucleolus,” like a nucleus, but no membrane separates it from the rest of the body. Too primitive for sex, procaryotes reproduce by simply splitting themselves in two.

The first of all life forms are procaryotes called Archaea (“Ancients”). They continue to thrive in the harshest of environments, like volcanic vents and acidic soils.

The other procaryotes are all the other bacteria, including Cyanobacteria that harvest solar energy by photosynthesis. They use water as fuel, splitting it with sunlight and combining it with carbon dioxide into fats and sugars. Importantly, photosynthesis releases oxygen gas as a byproduct. Cyanobacteria are still with us, blooming and rotting spectacularly in our fertilizer-laden runoff.

Procaryotes evolve slowly because they can’t exchange genetic material. But they reproduce quickly! If even only one splits into twins that also split just days later, its descendants multiply astronomically. No wonder cyanobacteria oxygenated the world, even if it took them almost a billion years.

Ancient cyanobacteria were too crude to handle oxygen, for them a deadly byproduct. But the ocean waters back then contained much dissolved iron, which sopped up the oxygen they released, making iron oxide – rust – that settled down to the seafloor. Today, these ancient “banded iron” deposits are mined for steel.

Around 2.3 billion years ago all the dissolved oceanic iron was used up. Oxygen began to accumulate in the atmosphere and ocean. Trouble for the procaryotes! Most went extinct. Others abandoned the surface environments they had polluted so thoroughly with their oxygen waste. They flourish in environments without oxygen like marshes, acid soils, or frigid lake bottoms. They also live in oxygen-free micro-environments like your own gut, helping you digest your food.

Humanity, take note: organisms can succeed so well they transform their environment so completely it becomes unlivable for them.

But succeeding life can then adapt to, and flourish in the transformed environment! Bacteria called “aerobes” invented a powerful new way to energize themselves: burning their food with oxygen.

Lynn Margulis

Reflecting the social unrest and struggle of the 19th century when poet Alfred Tennyson characterized Nature as “red in tooth and claw,” Charles Darwin’s evolution is driven by competition for limited resources like food or living space.

Lynn Margulis, a great scientist of our own times, discovered endosymbiosis, evolution’s most profound step. Symbiosis means “living together” – endo means “inside.”

It’s laughably gender-stereotypic that a man discovered competition as an evolutionary force, and a woman revealed the importance of cooperation, but there it is…

Male-dominated science extends beyond Darwin’s time into ours. As a young PhD, Margulis submitted “On the Origin of Mitosing Cells” to 15 journals before one published it. She had to defend her idea for many years before it was fully accepted – the scientific version of dancer Ginger Rogers matching Fred Astaire’s every step “backwards and in high heels.”

Our last foray introduced the “Gaia hypothesis” that the entire Earth and all her living cargo behave as a self-maintaining, living being. As an established scientist, Margulis developed it in collaboration with atmospheric scientist James Lovelock. Bi-gender science…

Endosymbiosis

About 1.5 billion years ago, Life fully adapted to the oxygenated environment when larger procaryotes started allowing smaller ones to live inside them as organelles (“little organs”) that cooperate for the collective good. Together, host and organelles constitute a complex eucaryote.

All eucaryotes have organelles called mitochondria, “little thready granules.” Descended from aerobes, they convert the host’s food and oxygen into energy the cell needs.

One of the most important roles the eucaryotes filled was to become havens for cyanobacteria fleeing the oxygenated environment. Now “chloroplasts” inside plant cells, they harvest sunlight for the cell. The oxygen they make, which cyanobacteria couldn’t tolerate, is absorbed and used by mitochondria. Cooperation for mutual survival!

About 800 to 600 million years ago, eucaryotes also developed “the urge to merge,” sexual reproduction, genetic-material exchange between individuals. That resulting in Darwin’s evolutionary explosion of many-celled beings like plants and us.

Epilogue

We started with Goldilocks; let’s end so children can understand:

“Once upon a long time ago, two planets were laid in orbit around the Sun.

“Venus didn’t hatch, but Earth did, and lives.” – Rappler.com

Born in Manila and educated at UP Diliman and the University of Southern California, Dr. Kelvin Rodolfo taught geology and environmental science at the University of Illinois at Chicago since 1966. He specialized in Philippine natural hazards since the 1980s.

Keep posted on Rappler for the next installment of Rodolfo’s series.

[OPINION] The paradox of the faint young sun, the origin of life, and the modern cell

In the beginning

The paradox of the faint young sun

How life made and keeps Earth livable

Lynn Margulis

Endosymbiosis

Epilogue

Previous pieces from Tilting at the Monster of Morong:

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