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For the astrobiologist Antígona Segura,
who knows about plants in other worlds

Bangia fuscopurpurea

Although dark matter exerts a gravitational effect on ordinary matter, we can’t observe it directly. That’s why we call it dark, but it might be more precisely described as matter that is invisible across the electromagnetic spectrum. Dark matter makes up eighty percent of the universe. Like agar culture medium, this is what holds things like galaxy clusters—and galaxies themselves—together.

We make our home within the Virgo Cluster.

In biology, the term dark matter is used for all the microorganisms we have not yet been able to isolate and identify. Holobionts—every body is an ecosystem, inside of which live, perhaps, more life-forms than there are stars in the universe.

Agar, or agar-agar, is derived from a type of red algae.

The wavelength of cyan is 476–497 nm. The word cyan derives from the Greek kyanos, which is sometimes translated as “dark blue.” You once read an article that said the ancient Greeks couldn’t see the color blue. The author cited as evidence some passages from The Odyssey in which the sea is referred to as “wine-dark.” Purple, not blue.

But then again, we have kyanos.

When they first announced the ATKIN-5 project, you were in the sea, which didn’t look blue to you either. This was the day you almost drowned. You were eleven, and you had swum out far from the shore. You remember the rise and fall, the salt on your face, and the piece of seaweed, of macroalgae, that you were playing with. You never saw the wave coming at you from behind. You didn’t see the next one either, nor the one after that.

“The samples taken by ATKIN-5 will allow us to determine whether there is life on Europa,” the project leader explained to the press, at the same exact moment your mother was trying to revive you on the beach. One of your obsessions from that day forward would be trying to make sense out of coincidences like this.

Corynephora marina

Approximately four billion years ago, in a hydrothermal vent rich in iron and sulphur, inert matter came to life for the first time on this planet. That first microorganism is known as the last universal common ancestor, or LUCA. In theory, LUCA is where we would land if we went far back enough in our genetic family tree. But it’s also possible that there exists a LUCA-2, a second common ancestor from which descended all the organisms we are so far incapable of detecting.

Life developing in parallel lines.

In the mid-nineteenth century, Anna Atkins used cyanotype to document the different forms of algae in Great Britain. Potassium ferricyanide—the Prussian blue trace of an organism that has long since turned to dust. For many years after her death, Anna Atkins fell into obscurity. Her work was almost entirely disregarded. Once, a Victorian academic even suggested that the AA that appeared in the volumes of British Algae stood for “Anonymous Aficionado.”

Every time you write about yourself, you use the second person. It’s the only way that makes sense to you. To talk about what happened to you, you need a you to encompass the I, which most of the time feels like someone else.

We search for life in other worlds on the basis of what we know of our own, but scientific paradigms aren’t infallible; we could be overlooking a key part of the story. For example, no one would have thought organisms could survive in a lake of sulphuric acid, but they can, and do.

When you were young, you couldn’t reconcile the idea that the woman whose depressive episodes would last for weeks was the very same woman who was strong enough to pull you out of the sea and bring you back to life. It’s such a monumental contradiction that you once forgot she was the one who saved you. You only began to understand one morning when you, now an adult, couldn’t get out of bed either.

Ghost population—the possible remnant of a long-extinct human group in our own DNA.

As the ATKIN-5 team tests its space probe in Antarctica, you are under the covers again, now a shadow of the melancholy that every woman on your mother’s side of the family must try to outrun. The tests at the South Pole fail, and it dawns on you, seventy-five hundred miles away and two days after your last shower, that you’ve forgotten the name of one of your great-grandmothers.

Ectocarpus littoralis

Terrestrial plants are believed to have descended from a group of green algae called Charophyta. Two orders of charophytes, Charales and Coleochaetales, are closely related to what were likely the first plants to spread over the earth’s surface: bryophytes.

Moss is a bryophyte.

Cyanophyta, or blue-green algae, are not in fact algae; they are bacteria. Cyanobacteria were the first photosynethic oxygen-producing organisms and, as such, had an important role in determining the course of life on earth. The oxygen content of the atmosphere is maintained at a constant 20.95 percent.

The sun is as necessary for photosynthesis as for the creation of cyanotypes and, although it may seem unrelated, you always enjoyed looking at moss up close and imagining you were zooming in on a forest from outer space.

No matter how hard you try, you can’t remember the exact moment you lost consciousness underwater, just seconds from returning to a state of inert matter, but even though you can’t access the information, it’s still in there, interfering with your other memories and causing you, on occasion, to lose your sense of space-time.

Sargasso is one of your favorite words, and you don’t know why.

Sometimes you’re able to function in what we call the present, but sometimes you get lost within yourself. The ATKIN-5 launch countdown begins and you, on a bench in the botanical garden, are struck with an unfiltered awareness of the sea of green surrounding you. In every chloroplast, a miniature thunderstorm.

Iridaea edulis

Overproliferation of algae can significantly reduce oxygen levels in water, leading to the death of entire populations of the other organisms that call it home. Climate change has led to more and more of these blooms, and more and more oceanic dead zones have appeared in recent years. The Capitalocene and its ironies: we can destroy new life-forms before we even discover them.

The pesticide Zyklon B is composed of cyanide impregnated into secondary materials such as diatomaceous earth, a sedimentary rock formed from the cell walls, or frustules, of millions of microscopic marine algae. The Nazis used Zyklon B in their extermination camps.

Sometimes it leaves a trace of Prussian blue.

The ocean is your obsession. You can’t stop talking about it, but even so, you remain at the edge. You’d like to learn to dive in, but you’re too scared. Every time you get close, you push yourself deeper into your prison of rituals and fixations, your supposed defense against this terrifying piece of you that threatens to burn down everything you love.

This paralyzing fear is the force that pulls you toward the bottom, making you see the things you’d rather ignore. Like the garfish thrashing around on the floorboards of the pier. On the ferryboat with your family, you thought about the sea needle’s last water-seeking gasps as it drowned in the air. A man had stepped on its mouth to keep it from flopping back into the water. The horror, the violence that is such a part of our world, the salt in your eyes, a fish that won’t die. The next day, you would be the one thrashing, under the waves.

The ATKIN-5 probe circumnavigates Mars to gain momentum toward Jupiter as you, millions of miles away, wake up again screaming.

Naccaria wigghii

Life springs from order and chaos, the product of a series of accidents and coincidences without which nothing would be as we know it. Two planets colliding, an atypical moon, tides that affect the rotation of the earth. The very same entropy that will one day consume the universe is what has allowed us to be here in the first place.

Cancer—a proliferation of cells reproducing uncontrollably, a survival impulse in overdrive.

Anna Atkins died in 1871. Various causes of death are noted, including paralysis, rheumatism, and exhaustion. She left her algae and fern collection to the British Museum.

Biological witness—a sample of algae, a moment in the earth’s history, told in cyan.

Sometimes you feel like you’re drowning again.

During your mother’s fifth chemotherapy session, poison drips into the line and through the cannula and you are outside yourself. You are overcome with the knowledge that one day you will lose your last link to this shared piece of your life stories. Your mind falls into a black hole at the exact moment ATKIN-5 begins its descent onto the surface of Europa. All you can think of as you run from the hospital is Moshio salt.

Salt made from algae, and the unavoidable fact that all things must end.

Polysiphonia subulifera

When the first photosynthetic organisms appeared on our planet, the ozone layer had yet to form. Life on earth began in the oceans in part because water, in addition to being a solvent, served to shield the first life-forms from the sun’s ultraviolet rays. These days, in our atmosphere, yellow photons with a wavelength of 560 to 590 nm are the most prevalent.

Our sun’s light determines the color of plants on earth. There could be other planets that revolve around a dim star with vegetation that live off of infrared light. In such a world, kelp forests would be black.

Black—a melancholy color, like blue. An inundating aqueous humor that leaves you, sometimes, unable to breathe. You have turned your mother into a specter that haunts you, that tries to drown you, so you won’t have to face the fact that the only one holding your head underwater is you.

An experiment carried out on the International Space Station showed that algae, unlike us, can survive in space.

After many years, you and your mother return to the beach where you almost drowned.

She lies back in the shade, and you go down to the water. The story, with some differences, repeats: you swim up to the point where the waves crashed into you when you were young, and you are surprised to find your feet touch the bottom. It makes sense, but you still weren’t expecting it. Like you weren’t expecting how quickly you would reach the age your mother was when she rescued you. She couldn’t help you now, not anymore, even if she tried. She’s sleeping in the shade, a silk handkerchief tied over her bald head.

The uncertainty of death means it doesn’t even come when you’re expecting it.

Thousands of nanorobots emerge from ATKIN-5 to traverse the frozen surface of Europa. Below the ice lies an ocean whose tides are pulled by Jupiter.

Sargassum vulgare

Most of the oxygen we breathe is produced by microscopic algae called diatoms. Their silicon skeletons are formed from minerals deposited by rivers and glaciers into the oceans. The dust of our ancestors’ bones, our crumbling mountains, all flows back into the sea. When diatoms die, their skeletons are laid to rest on the sea bed.

Much of the salt we consume comes from a prehistoric ocean.

Broadly—and imaginatively—speaking, we might say our ancestors are what sustain us. The rocking of the waves, the salt in your hair, the algae-covered rock you’re sitting on. You become aware of the fact that you are a small piece of an indifferent universe in which nothing goes to waste, and you smile.

Dark matter—everything that exists on the edges of the story you tell youself to keep the illusion of continuity alive. The blind spots, the ambiguities, the ghost-memories; a biography made up of nothing more than a collection of disjointed notes on the back of an algae catalogue.

(Any relationship between headings and the rest of the text is purely accidental.)

A nanorobot pokes through a crack in the ice, takes a sample of orange material, and analyzes it. And twelve hours later, at long last, the ATKIN-5 team receives the message they have been waiting for.