The Life of Earth : a very short version, according to science.

Preface, part 1:

I am a human with curiosity, wide-eyed wonder, a dab of faith, and an interest in learning and discovering more about our peoples and planet and and surrounding celestial bodies. I am Christian and this is a short version of Earth’s Life as presented and best understood through most accepted science textbooks.

I have many questions about the origins, age, and lifespan of this planet.

Faith is not something, by definition, that can be proved.

So I won’t try to prove it by putting my faith up against science. I believe that life on this planet and in this universe has the guidance, or benevolent machinations of a supernatural figure involved in the mix somewhere. I believe that this entity, G*d, has a deep love for this planet and for the life forms contained on it. Beyond that, my questions multiply. So this is a very short version of what most scientists consider to be Earth’s story.

Preface, part 2:

This is not about the origin(s) of the universe or earth. It is about the life history of earth since it existed, in rough chronology, to the extent I understand it after having read a bunch of science stuff from a bunch of different places and not understanding most of it. These are weighty matters - and often interesting ones! - that we discuss frequently with our children. Again, our root system is based on a faith, and it is also based on incessant curiosity and pursuit of truth. In our household, the worlds of science and reason are not enemies.

You can study music and dissect it down to its smallest parts, yet when you try rebuild an ephemeral piece that possesses a staggering beauty, it is impossible. You may get 99% of the way there as you try and rebuild the whole from its parts. But somewhere in the in between, somewhere in the cracks, is what some might call the soul; that mysterious matter that blends those reducible atomic parts into something magnificent…and that defies a complete deconstruction. At least that’s my take. Music is made up of mathematics, yet mathematics doesn’t fully explain the magic of mystery.

The world and its history and phenomena can be reduced and explained through science, which is beautiful…but for me, when those pieces are built up again, there’s still enough missing notes and magic in the cracks to keep a tiny part of my brain space available to believe that something beyond huge passages of times and swirling gases is also floating in the mix somewhere.

That’s my take today anyway. Enjoy, and if nothing else, ya gotta admit the whole idea of the Geologic Time Scale is amazing.

Joseph

First : a few notes on geologic time scale (GTS)

Paleontologists, geologists, and earth scientists use the GTS system of chronological dating in talking about events in geologic history. The main divisions of big time that science uses for Earth’s history go like this:

An eon is a super-huge massive chunk of time. Around a billion years. Science has divided Earth’s history into four eons.
An eon is divided into eras.
Eras are divided into (geologic) periods.
Periods are divided into epochs.
Epochs are divided into ages.

Birth of a sun.

Pop quiz: which star is the most important one to Earthlings?
Score if you said “our sun!”
We need our sun for warmth and for heat. We literally would not exist without it.

So somewhere in the chronology of existence, the Sun was born. How long has the sun been around, and how did the sun come to be in the first place? We’ll save that for other discussions.

If you’re most scientists, you believe the Sun came first, then the Earth.
If you’re most Christian theologians, you believe the Earth came first, followed by the Sun.

Again, that’s a different discussion. I’ll probably have to write that a lot.

It’s not the only sun in the universe. In fact, it’s not even the biggest or brightest by a long shot. But it’s super important to us. By “us” I mean all life forms living on Earth. There would be no life if our Sun didn’t exist (see: pop quiz above).

Our Sun is one of billions of stars swirling around in our galaxy.
There are trillions of galaxies whirling around the universe.

So do the math. Or don’t. There’s a lot of stars in our galaxy, and there’s a lot of galaxies in our universe, and…who knows: maybe there’s a lot of universes in a larger multiverse…

Bottom line is : thank goodness for our Sun. Without its light and warmth, we wouldn't be around.

Birth of an Earth.

We’ll skip to the point of Earth and Sun co-existing happily. By co-exist, we of course mean that Earth needs Sun to survive, but not the other way around.

At 93 million miles away, Earth is the third planet from the Sun. One of eight or nine. That’s another discussion too.

Earth rotates (spins around) on its axis once every 24 hours. That’s one day.
Earth revolves (orbits) around the Sun once every 365-ish days. That’s one year.
So Earth hurtles around the Sun at around a thousand miles a minute.*

(That’s over 60,000 miles per hour.**)

The Moon revolves around Earth every 29.5 days. Oh yes, somewhere in the continuum of time, Earth’s Moon is born.

Fun fact: the Moon rotates at the same rate it revolves.

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*1,100 miles per minute
** 66,000 miles per hour

Hadean Eon : dust and gas and igneous rocks.

So scientists mostly agree that Earth was originally a big ball of matter and not much going on. Hot lava and liquid rock.

As the surface cooled over time, that liquid surface began to solidify and became what we now call igneous rocks.

Igneous : from the Greek word for “fire”

No life forms exist at this point.

Archean Eon : topography and metamorphic rocks.

Deep from Earth’s interior, heat spread out, driving up the crust in different regions and forming mountains, valleys, basins, gorges.

As Earth was slamming and pushing together, the heat and pressure morphed igneous rocks and others into a different sort of rock: metamorphic.

Metamorphosis : comes from the Greek “changing form”

No evidence of life forms exist from this time. Doesn’t mean it didn’t exist. Just means there’s no evidence of it.

Proterozoic Era : water and sedimentary rocks.

Water pours down from clouds and finds its way down mountains and gulches, creating rivers and streams and carrying sand, gravel, and tiny particles of rocks in layers to ocean floors.

Over time, those layers hardened into a type of rock called sedimentary.

Scientists have determined that evidence of life forms exists in the form of microorganisms during this part of Earth’s life, now known as the Proterozoic Era, which means “early life”).

Archean Eon > Proterozoic Era

Paleozoic Era : Invertebrates and Multicellular Organisms.

Cambrian Period.

We are now in the era of life thriving, according to records found in fossils. “Thriving” may be an exaggeration: the life forms are invertebrates. All live in water are led by the mighty trilobites. Segmented worms are apparently frequent guests as well.

Ordovician Period.

Kings don't stay kings forever: Cephalopods take over trilobites as the most dominant form of life. This family would include squid and octopus. Fish become more plentiful and moss and lichen, on land, begins to appear. Bivalve musks and gastropods are also popular attractions.

Silurian Period.

Land rises. Seas fall back and leave salt deposits. Cephalopod kings get displaced by sea scorpions. Jawless fish drop in now and then.

First evidence of vertebrate life, in the form of fish.

Archean Eon > Paleozoic Era

Paleozoic Era : Amphibians, Reptiles, and Big Vegetation.

Devonian Period.

Land plants start taking over and Earth is looking green! It’ll stay that way forever, right?

Cute little ferns creep along the forest floors and larger vegetation begins stretching, growing up toward the sun as they develop roots systems.

More fish, lots of fish, including some that develop lungs and start muddling around from water hole to water hole.

Carboniferous Period.

Huge swamp forests carpet Earth. Also known as The Age of Plants, or less catchily, as The Coal Age, because, well…where does coal come from?

Yeah, the coal we use today comes from those grand old plants from another era.

Also, amphibians, which are a vertebrate, show up. Amphibians split their lives between land and water.

Permian Period.

Climate turns try, mountains rise high. Big trees replace little ones, reptiles take over amphibians as dominant creatures.

At the end of this period, we have disaster…

…a mass extinction. Yuck. Possibly caused by too many volcanic eruptions. And thus a period - and era - dies.

Archean Eon > Paleozoic Era

Mezozoic Era.

Triassic Period.

Aah, now we’re into the super fun part : dinosaurs! The climate’s warmer, waters are moving down the mountains, and we got some walkers. Reptiles are still the big dogs. But sadly, there’s no actual dogs at this point.

Archean Eon > Mezozoic Era > Triassic Period

Jurassic Period.

Toasty warm, just right for the dinosaurs in all their walking, now-flying glory. The big mamas are the plant-eaters, but of course they’re not the scariest. There’s a few mammals roaming around, which is great for the non-vegetarian dinos.

Archean Eon > Mezozoic Era > Jurassic Period

Lower Cretaceous Period.

Plants start to appear. Seas and mountains on the move. Reptiles still top dog. Again, no actual dogs.

Archean Eon > Mezozoic Era > Lower Cretaceous Period

Late Cretaceous Period.

Temp is dropping, as are seas. Then, an unfortunate thing happens. What I mean by “unfortunate” is that something kinda bad happens. That kinda bad thing is a massive meteor that hits Earth and quickly makes a bunch of species extinct. Super sad.

Archean Eon > Mezozoic Era > Late Cretaceous Period

Cenozoic Era : Recent life.

Paleogene Period.

So the climate’s hot again. Remember, it was chilly for a while in the last Era, and some sad stuff happened, like all the dinos dying and most other life forms. But now it’s hot again. There’s a bunch of forests and reptiles aren’t the top dogs. Mammals are up at the top of the food chain, or at least the most prevalent.

Partway through this period, the climate cools a bit, allowing for the spread of grass and plants. Mammals dig this and eat up.

Paleocene Epoch
Eocene Epoch (Dawn of recent life)
Oligocene Epoch

Neogene Period.

If it feels like the climate is yo-yo-ing around, then this might be surprise you: things continue to warm up, rather than reverse themselves repeatedly. This means more stuff growing, which changes mammals’ eating habits. Some of them grow big and strong because they eat their vegetables, or whatever healthy stuff their mamas are making them eat.

If you read the previous paragraph carefully, you might have noticed that things were continuing to warm up, and this might have surprised you. In the later part of this Period (the Pliocene Epoch), things start to cool down again. Not crazy crazy cool down, just some mild glacier kind of situations. Things are still comfortably warm in some places you might be familiar with, like North America.

Micene Epoch
Pliocene Epoch

Quaternary Period.

Those glaciers are scraping their way southward and digging up some land, which makes it possible for enterprising individuals to get places they might not have otherwise (see: Bering Land Bridge). This time in history is named after the Denis Leary movie trilogy Ice Age, and is called “the Ice Age.” They move and melt, move and melt, move and melt.

Humans are around and on the move. Note: that’s us.

Eventually, that brings us to the Holocene Epoch, which is where we’re at now. The Age of Humans and defenders of poor defenseless Earth. We figure out how to make fire and build weapons out of stone, and a little while later, figure out how to make atomic bombs and use silicon chips. In between, there’s some learning about other stuff, like using wheels and animals and farming. These discoveries and inventions lead to the development of societies built around villages, towns, and cities, and these eventually grow into civilizations and ways of living.

As people live together and bounce ideas around, technology progresses and allows for longer travel and easier migration. Languages are developed and people are able to communicate with each other and record history, which is helpful for historians trying to figure out what happened long ago.

Finally, all the continents except for Antarctica are settled and divided amongst countries in some form. There’s lots of wilderness and mountains and trees and plenty of room for humans to build and live.

Until the humans keep coming and coming, and growing and growing, and building and building and figuring out new ways to send byproducts of technology into the atmosphere and into the ground and into the ocean.

We are still here, and still learning how to get Earth healthy again.

So that brings things up to speed. Welcome.

Pleistocene Epoch
Holocene Epoch : Age of Humans!

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Quick summary of Earth’s geologic history according to the GTS:

Note : sometimes the first three Eons are lumped together and referred to as the Precambrian

Hadeon Eon
Archean Eon
Proterozoic Eon
1. Paleozoic Era (“old life”)
  1. Cambrian Period
  2. Ordovician Period
  3. Silurian Period
  4. Devonian Period
  5. Carboniferous Period
  6. Permian Period
2. Mezozoic Era (“middle life”)
  1. Triassic Period
  2. Jurassic Period
  3. Lower Cretaceous Period
  4. Late Cretaceous Period
Phanerozoic Eon
1. Cenozoic Era (“new life”)
  1. Tertiary Epoch
    1. Paleocene Epoch
    2. Eocene Epoch
    3. Oligocene Epoch
    4. Miocene Epoch
    5. Plicocene Epoch
  2. Quaternary Period
    1. Pleistocene Epoch
    2. Holocene Epoch…