A lobe-finned fish swims in a shallow sea, Breathing in air from under the water. But this fish travels up to the surface, To breathe the oxygen-rich atmosphere, To feel the air above the limpid sea, To see the sun shining on the green land. Its stubby fins propel it through the sea, Until it reaches water choked with mud In a dismal swamp. It cannot swim now, So, with its fins churning the mud, it walks, Feels the soft sea bottom beneath its fins, And slowly heads for the nearest shoreline. Inch by inch, step by step, it moves forward Through the dark, murky waters of the swamp. Its head surfaces; it gulps the fresh air. Soon the rest of its body surfaces, And now the creature steps onto dry land, Ready to walk beneath the forest trees. Other walking fish step onto dry land, Following the first brave adventurer, That gave up swimming and began to walk. Their descendants will make the land their home, Only going back into the water To lay eggs, birth a new generation. Their descendants will be amphibians. Their fins will evolve into sturdy limbs, Lungs will become more sophisticated, And skeletons will become heavier, Enabling them to colonize more land, And soon give rise to other tetrapods. But these tetrapods do not exist yet. Giant amphibians rule over Earth, New top predators on land and in sea, Preying on giant arthropods and fish, Clinging to the soil with their large, clawed feet Waving or dragging their muscular tails.
Giants of the Forest The first animals to colonize land Are insects, arachnids, myriapods Their ancestors crept out of the ocean. Now, they crawl or fly through the lush forests, Breathing in large amounts of oxygen, Which makes them grow to an enormous size. Giant millipedes crawl beneath the trees, Feeding on mosses and on leaf litter, Segment by segment passes on the ground, Seeming to flow over leaves and tree roots, Slithering back and forth along their trail, A lengthy, black serpent with many legs. Sea scorpions hide on the ocean floor And at the bottom of rivers and lakes, Using the spines upon their legs to move And gather food from the brackish water. Land scorpions scurry under the trees, Capturing other insects with venom. Enormous griffinflies and dragonflies Hover in the sky, beat transparent wings, Stirring up a breeze in the humid air. They lay eggs upon the water’s surface, Swoop down on smaller insects for their prey, Look down on other insects from up high. These share the forest with other creatures, Creatures that inhabit the Earth today. Spiders spin webs, silken traps for their prey. Cockroaches and termites swarm on the ground. Six-winged insects fly in the warm air. Ancestors of grasshoppers feed on plants. Beetles and flies evolve close to the end Of the era, but they are much smaller Than other arthropods which came before. The climate is dryer, the forests die, Less oxygen is pumped into the air. The age of giant arthropods is done.
Fish and Sharks New animals evolve under the sea: Sleek animals of bone or cartilage. New animals hungry for flesh and blood, Or feeders on green algae and seaweed. Streamlined, fast-swimming creatures of the deep: Fish have appeared in the ancient oceans. Many jawless fish hunt prey or scavenge. Lampreys feed on the blood of other fish, Hagfish devour the underwater dead. They share the sea with eel-like conodonts, And ostracoderms with armored bodies, Undulating gently with the currents. Over millions of years, jawed fish evolve: Armored placoderms, with paired pelvic fins, Bottom-dwellers, living in shallow seas. And armored spiny sharks, with bonelike scales, And chimaeras, ghost sharks, with fused jawbones. Not real sharks, but still aquatic hunters. Through the sea, the real sharks hungrily swim, Moving side to side, eyes upon their prey, Or smelling their prey’s blood in the water. The fastest fish flee from the predators, But the unlucky victims are swallowed By wide-open jaws lined with pointed fangs. The sharks, over time, have new prey to hunt: Bony fish with their harder skeletons. Ray-finned fish, which will be so numerous That they will spread from seas to freshwater, And lobe-finned fish, with thick and stubby fins, Which will crawl onto land in the future. Yet now the lobe-finned fish stay in the sea, Preying on smaller fish, preyed on by sharks. Sharks, top of the underwater food chain, The fiercest predators to swim the seas. Hunt or be hunted is now the main rule For contact between predator and prey.
The Green Land Though the seas are crowded, teeming with life, The land is barren rock and sand and dirt: Silent and grim and inhospitable, Until, suddenly, out of the water, Come tiny green algae cells, forerunners Of an invasion of the land by plants. Algae and mosses and tall, tree-like ferns Send their spores over the bare land to sprout And stake their claim, invading so quickly That in millions of years, forests have formed Of horsetails, club mosses, and tree-like ferns Waving their fronds in the tropical air. The forests breathe, filling the atmosphere With fresh, pure, life-giving oxygen That will cause changes in land animals: Expansion of their lungs and their bodies. Soon, giants will walk under the tall ferns, Or fly above the dense, green canopy. The air is warm and wet under the fronds Of giant ferns and horsetails, and beneath The branches of smooth scale trees and club trees. Down in the ancient, living, breathing swamps, Spores float, land, and sprout, but where it is dry, The plants send out a new invader: seeds. Seeds growing in cones, borne upon the wind, Give rise to ever-newer forms of plants, The hardy gymnosperms: hard wooden trunks And needles for leaves, both adaptations To possible disasters which may come Upon this green land, ancient paradise. Disasters which may scorch and dry the land, And bury the ancient forests in dust, Crushing them down, over millions of years, Into black lumps of rock, to burn in fire. But at the present time, the forests live, Stretch up to the sky, shade the land, and breathe.
The Ancient Seas
The ancient seas surround one continent, A giant landmass, ancient Gondwana. On sea and land, the sun beats down and warms The planet’s surface, where little changes. But beneath the waters, life is thriving: Diversity which will not come again. Under the oceans, the trilobites rule. Their kingdoms are the floors of shallow seas. Crawling upon the sandy sea bottom, They hunt down worms for prey, or filter-feed On plankton, algae, tiny forms of life, Found buried in the sand, or floating free. Throughout the water, the jellyfish swim, Drifting lazily in the open sea, Or through forests of sponges and corals, A living, breathing aquatic garden. They wait for prey to swim within their grasp And capture them with stinging tentacles. Graptolites are anchored to the sea bed, Or float with currents through the deepest seas, And ten-armed sea lilies and feather stars Sway and wave their arms on the ocean floor, Filtering food from the upswelling waves, Gathering plankton from the deep water. Brachiopods inhabit shallow seas, Hiding within their unhinged shells, sharing Their habitat with ancient ancestors Of oysters, chitons, octopi, and snails, And with the backward-swimming nautiloids, Floating free within their chambered shells. Creatures of solid shell and carapace, That crawl or swim or rest on the sea floor Or soft-bodied creatures that drift and sway With the swelling, sweeping ocean currents. All call the sea their home, this ancient sea: A life-filled, underwater paradise.
Under the Earth’s frozen, icy surface,
Heat and pressure build up until the ice
Begins to crack, and smoke and lava pour
From underground, erupting volcanoes.
Carbon dioxide fills the atmosphere,
Causing it to trap the sun’s rays again.
The atmosphere absorbs more solar heat,
And more volcanoes push up through the ice,
Releasing even more warming gases.
At last, the ice begins to melt away.
The oceans, streams, and rivers start to thaw.
The life beneath the seas starts to wake up.
Earth’s Snowball phase is ended, and its ice
Has melted, is a distant memory,
When new forms of life begin to appear,
Larger, multicellular, specialized.
Though microbes have survived the long winter,
They share the oceans with new forms of life.
The first multicellular animals
Have now evolved and float throughout the seas,
Thanks to rising warmth and high oxygen.
Soft-bodied animals of many shapes
That drift through the water, much like microbes,
And feed by filtering out nutrients.
All at once, new life forms quickly evolve,
So fast, indeed, that in the far future,
Their appearance will be named “explosion”.
Not a violent explosion, with bright fire,
But one as deadly as a volcano
To the drifting, soft-bodied animals.
These life forms go extinct but are replaced
By distant ancestors of life today:
Ancestors of insects and crustaceans,
Of all worms, spiders, mollusks, and starfish,
And even of chordates. The stage is set
For animals to inherit the Earth.
Of doing nothing
Now rocks absorb the carbon dioxide
From the atmosphere, drawing it downwards
Into the Earth’s crust. As it leaves the sky,
So does the warmth that envelopes the Earth,
Rays of the sun previously welcome
Are now repulsed, now flung back into space.
Bitter winds whistle over the still world,
Bringing snow, a swirling, whirling blizzard
That blankets the whole planet. Piercing cold
Hardens the water: liquid freezes up.
Ice crackles on all water surfaces:
Lakes, streams, rivers, even the mighty seas.
Two massive, looming walls of solid ice
Stand at the poles, reflecting the sun’s rays.
As ice spreads farther, the walls start to move
Crawling towards each other through the deep snow
Until they touch, meet at the equator,
Burying Earth under a huge ice shield.
Ice blankets the water and continents.
Beneath the ice, all sleeps, now motionless.
The little people who lived here before,
All the little microorganisms,
Are still: no longer eat and drink and breathe.
The planet seems bare and lifeless once more.
Yet life is not gone; somewhere far beneath
The thick, crushing layers of deadly ice,
All the little microorganisms
Are huddling, now, deep in their winter beds.
They hibernate, sleep, patiently waiting
For the ice to melt and spring to return.
They wait and wait, but no spring ever comes.
No friendly warmth remains on frozen Earth.
The planet is a ball of solid ice,
A snowball orbiting the useless sun,
Which has no power to break the ice shield
And end the planet’s million-year winter.
The ice melts, the planet warms up again.
Spores of bacteria reawaken
In a barren world of water and rock,
In an atmosphere full of oxygen.
Life evolves slowly for a billion years,
But the Earth’s surface undergoes changes.
Hail, Columbia, most ancient of lands,
Supercontinent of young land masses.
But far beneath the surface of the Earth,
The pieces of the crust, tectonic plates,
Crawl past each other, move towards each other,
Causing the planet to tremble and quake.
Columbia breaks up, land masses drift
Away from each other, sailing the seas,
Which steam as molten lava is released
By new volcanoes and rifts in the Earth.
Chaos reigns upon the planet’s surface,
But its life forms continue to hold on.
Colonies of breathing blue-green algae
Still huddle together underwater,
Releasing oxygen into the air.
Aerobic bacteria thrive in it,
While anaerobes underground hide from it.
Life survives, but does not change for eons.
But the surface of the Earth also lives.
What will later be North America
Is cracked in half: a rift splits it apart,
And rivers of lava flow through this crack.
Now Rodinia, a larger land mass,
Forms: continents come together again.
And so it happens for a billion years.
New land masses form, others break apart.
The planet warms and cools alternately,
As volcanoes release warming gases,
Or these gases are absorbed by the rocks.
No boring billion years for Earth’s surface.