Happy Earth Day!

Whenever I need to be reminded of how special and unique the Earth is I look up at the moon. While the planet's only natural satellite possesses a beauty all its own, you can't open the door and go for a walk there. Nothing blooms. There's no air. No blue skies. No protection from falling meteorites or dangerous ultraviolet (UV) radiation from the sun. It gets hot enough for your blood to boil and cold enough to turn the carbon dioxide in your breath to ice. Even if you're suited up, you still have to be wary of moon dust, which not only irritates the lungs but creates toxic free radicals that can damage human DNA and increase the risk for cancer.

This is an artist's view of the early Earth shortly after its formation 4.6 billion years ago, when much of the planet was molten. (CC0 1.0 / Wikipedia)
This is an artist's view of the early Earth shortly after its formation 4.6 billion years ago, when much of the planet was molten. (CC0 1.0 / Wikipedia)

Long ago, Earth was no paradise either. The planet formed 4.6 billion years ago from ices and minerals in a dusty disk orbiting the nascent sun. Gravity worked its magic to pull the material together into a planet. As the early Earth grew from impacts and gravitational contraction, it heated up and melted. Volcanoes released some of that internal heat while also creating the first atmosphere from expelled water vapor, methane and carbon dioxide.

Craters define the moon, where they number in the millions. Most of them are several billions of years old, preserved through lack of erosion and a stable crust. This photo of the waxing crescent was taken on April 19, 2021 (Bob King)
Craters define the moon, where they number in the millions. Most of them are several billions of years old, preserved through lack of erosion and a stable crust. This photo of the waxing crescent was taken on April 19, 2021 (Bob King)

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During this time, a barrage of asteroids battered the Earth, moon and other planets and ploughed out too many craters to count. Many are still still vividly evident on the moon even in a pair of binoculars. With its unbreathable atmosphere, nonstop volcanic activity, heavy rains (as the water condensed and fell to fill the early oceans) and continuous meteorite bombardment, our planet fit the definition of hell to a tee.

But Hades slowly became the heaven we know today. The planet cooled. Weather, water and Earth's shifting crust erased most of those early impact scars. Today, just 190 confirmed impact structures have been identified from the millions of gouges that once riddled the planet's crust.

Stromatolites, like the specimen shown here, are among the oldest fossils. They were formed by photosynthesizing bacteria, which cemented sand and other materials into thin layers called microbial mats. (Bob King)
Stromatolites, like the specimen shown here, are among the oldest fossils. They were formed by photosynthesizing bacteria, which cemented sand and other materials into thin layers called microbial mats. (Bob King)

Through it all, life not only appeared but evolved. The oldest fossils of single-celled, bacteria-like organisms go back 3.5 billion years. About 3 billion years ago, some of those bacteria developed the ability to turn sunlight into chemical energy to build sugar and starches, excreting oxygen as a waste product. Earth's atmospheric began to fill with the exotic new gas that would make our arrival, in due time, possible.

About 2 billion years ago, separate, individual cells joined forces to form compound cells with many parts called eukaryotes. These evolved and diversified into three great kingdoms of organisms: bacteria, archaea (bacteria-like organisms that live in extreme environments) and eukarya (plants, fungi and animals).

Swirling with clouds, bountiful with life, the Earth defies the void in this satellite image made in April 2015. (Ocean Biology Processing Group at NASA's Goddard Space Flight Center)
Swirling with clouds, bountiful with life, the Earth defies the void in this satellite image made in April 2015. (Ocean Biology Processing Group at NASA's Goddard Space Flight Center)

Thanks to the microscopic machinery of photosynthesis, oxygen now comprises 21 percent of the air we breathe and life, both microscopic and macroscopic, carpets the planet. It's been a long road with no end in sight. Even if the current climate crisis alters Earth's weather for the next million years and wreaks havoc on humanity, life will persist. It's been through hell before and came out kicking. It will again, with or without us.

Of course, I hope it's with us. Humans have the transcendent ability to look at life from a distance and appreciate its specialness. With this knowledge we can protect and further the most precious thing the universe has ever concocted. In case we forget why we're here, a lifeless globe hangs overhead to remind us.

Several prominent craters stand out on the waxing gibbous moon Thursday night, April 22. They range in size from 20 miles (32 km) across for Kepler to 162 miles (260 km) for the Bay of Rainbows, also known by its Latin name, Sinus Iridum. The southern or bottom part of the moon is thick with craters, which make for a spectacular sight in a small telescope. (Virtual Moon Atlas)
Several prominent craters stand out on the waxing gibbous moon Thursday night, April 22. They range in size from 20 miles (32 km) across for Kepler to 162 miles (260 km) for the Bay of Rainbows, also known by its Latin name, Sinus Iridum. The southern or bottom part of the moon is thick with craters, which make for a spectacular sight in a small telescope. (Virtual Moon Atlas)

That's why I'd like to encourage you to observe the moon on Earth Day. Each orb defines the other's unique qualities. Several prominent craters come into view that are large enough to see in binoculars — Plato, Copernicus, Kepler, Tycho and a huge, former crater half-flooded in an ancient lava flow called the Bay of Rainbows. Think of them as fossils from an earlier time long before humans were even a thing.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.