This episode is sponsored by Squarespace.

Go to squarespace.com/microcosmos to get a free trial and 10% off your first purchase of a website or domain. Our Master of Microscopes, James, seems  like a tough person to get a gift for.

Like, what do you get the person who has the entirety   of the microcosmos available to him  with just a glimpse through a lens? But one of his friends and frequent  collaborators Professor Genoveva Esteban   sent him a gift for his 34th birthday  that seems especially difficult to top: she sent him a ziploc bag full of white  sand from the Marshall Islands All of the samples we are looking at  today come from that bag of sand,   which means that they all have their origins in  this archipelago that lies in the Pacific Ocean. The existence of the Marshall Islands is  intimately tied to life in the oceans around them.

For example, you may have heard of a place called  Bikini Atoll, a name immortalized by a style   of swimsuit and referenced in a popular cartoon  revolving around a sponge who wears square pants. Bikini Atoll is one of 29 atolls  that make up the Marshall Islands. And atolls like it are distinctive in  part because they are shaped like rings,   the result of a process that  spans millions of years.

These atolls begin as volcanoes that rise  from the ocean floor to become islands and   provide the means for corals to form a reef  around them that’s separated by a lagoon. Over time, the island sinks and erodes  away, leaving behind the reef and a lagoon. Then, the reef animals die and decay,  and waves break them up into sand that   can accumulate into an island, creating the atoll.

And so as we sift through the sample that James  has received, what we’re potentially observing is a   spectacular example of the way that geology  and biology are intertwined on our planet. Are we looking at land? Or are we looking at an organism?

The answer is yes, but with many  mysteries and question marks – like the samples we’re showing you now,  which we do not know how to identify. They lie outside the considerable expertise  of James, though he did have some guesses. If any of you have more specific ideas about what we might be watching right now, we would love to hear them.

James suspects these might  be large, eroded pieces of coral. And this shining bit of red  material might be some minerals,   perhaps bits of red rock that  James could see in his sample. This…well, James doesn’t know, but he  found a couple of them in his sample.

And it looks a lot like a tooth, though  we do not know if it actually is one. Bikini Atoll, and the Marshall Islands,  are also well-known for another reason. Between 1946 and 1958, the islands were the   site of 67 nuclear explosive tests  carried out by the United States.

Twenty-three of those tests  took place on Bikini Atoll,   and 44 were near another  area called Enewetak Atoll. Those atolls had been previously  evacuated, but the tests performed   on them still impacted people  living in the Marshall Islands. A 2004 report by investigators from the National   Cancer Institute estimated that 20 of  the tests exposed populations on nearby   atolls in the Marshall Islands to  measurable radioactive fallout.

That, has led to health  impacts that continued to   affect people long after the nuclear tests ended. The samples that we are looking at cannot speak to the impacts the tests have had   on the people who call the Marshall Islands home. James’ friend verified that these samples were  not radioactive before sending them to him.

But in the same way that the islands are an  embodiment of the life that surrounds them,   their sediments are a record of  the way we interact with that life. In James’ samples were beautiful foraminifera,   like the spiral you see at  the center of the screen now. Foraminifera are amoeba-like  single-celled organisms that   have encased themselves in  a hard shell called a test.

And when they die, those shells  become part of the world around them,   even becoming a major component of sand  in the western and Pacific atolls. The chemistry they leave behind  in those remains is a little   history of the world that the organism lived in. In 1946, a study of Bikini Atoll led to the  collection of different samples around the lagoon,   producing around 900 sediment samples  that revealed the presence of bodies   and remains of various organisms  including coral, algae, mollusks… and yes, foraminifera.

And scientists are still using  populations of foraminifera in   the area to study how humans  are shaping the local environment. In 2010, scientists published a study   on foraminifera in the Majuro  Atoll in the Marshall Islands. They found that some of the genera they  were studying declined in number as they got   closer to the more densely populated islands,  though other genera did not seem as affected.

One possible explanation is that the  species whose population densities were   lower near populated islands were  dealing with a surprising issue: an abundance of nutrients in the water. Now, you might expect nutrients to be good for  organisms, but the challenge for these   particular foraminifera is that they rely  on symbiosis with algae living within them,   exchanging various advantages with one another— like food. But, with an abundance of nutrients  in the water, the algae no longer need   their amoeba hosts, making the area  less welcoming for the foraminifera.

That is one of the ideas. But of course, there are  other potential explanations. And the bigger question is how this  will shape the islands in the years to come.

If organisms like the foraminifera  make up so much of the island,   what happens when their numbers go down? Or is there some larger pattern at  work, one we cannot see from the inside— a pattern made up of small actions  and even smaller creatures,   and woven together over millions of years— a little gift left by time for someone else to unwrap? Thanks for coming on this journey with us as  we explore the unseen world that surrounds us.

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