By CLARA DANHOF
for the shell-bearing organisms of the oceans, the increasing levels of carbon dioxide dissolving into the ocean are an existential threat to their existence. it dissolves them, dissolves their dead brethren from the ocean floor too, one molecule at a time until all that is left are the last traces of organic matter, are parts buried deep enough to be protected from the acidic water above.
the more carbon dioxide enters the atmosphere, the more enters the ocean, the more acidic it gets. the more carbon dioxide enters the atmosphere, the higher the carbonate compensation depth reaches.
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we dissolve our records of where we used to be, leaving behind nothing but a siliceous ooze, the last materials of the far off continents, only the pieces both strong enough and fine enough to have travelled so far.
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the continents grind into each other and if you are willing to subscribe to a flight of fancy, you can know that one day it will all be continent, that there will be nothing left of ocean crust.
ocean crust is melted mantle, and continental crust is melted ocean, so as long as ocean crust melts, which it always will for a given value of always, there will one day no longer be any ocean crust to melt, nowhere for ocean crust to form.
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the amount of meltwater off the east antarctic ice sheet has not significantly increased over the past decades, allowing it to appear for all the world that this ancient pile of ice is unaffected by climate change.
what remains unclear is how the relative sublimation off the ice sheet has changed, the loss of ice directly to the atmosphere.
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the continents grind against each other and churn each other into mud and muck, cycled and recycled and remade from the most basic ingredients for all the time there is to be had. the oceans come and go with all the ease of a season and the continents might remain, but that doesn’t mean their material doesn’t change.
if you take a continent and replace it rock by rock, just one at a time until there’s not a single piece of original material left, is it really the same continent at all?
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dendrochronology: the scientific method of dating tree rings to their exact age. by using multiple trees, you can create records thousands of years long and learn about local climatic conditions for the entire duration.
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an ocean sediment core will record no more than two hundred million years of history, which may sound like a lot but on a planet four and a half billion years old it’s nothing, it’s a grain of sand on the beach, a drop of water in a bathtub.
by examining such sediment cores, we gain incredible insight into the nature of the planet and into the nature of its past. we track glacial floods by the red clays in the western margins of the north atlantic, track changes in the salinity of the indian ocean by foraminiferal assemblages, track temperature in ratios of magnesium to calcium.
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the best climate records are in tree rings, the relative sizes of which can be aligned to produce an unbroken record. the question is, how old is the oldest tree stump?
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the earth is a lot better at recycling than we are.
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the oldest existing earth materials are zircon crystals from australia’s jack hills. they are dated at four billion and forty million years old; there may be older earth materials but we will never know of them, likely. to be dated, it needs to contain a radioactive element with a long half-life.
zircons are among the most resistant of earth materials.
they produce a conundrum.
the faint young sun paradox exists because the sun during earth’s early two billion years should have been too weak for liquid water to exist at earth’s surface, but the isotopes found in the jack hills zircons indicates that liquid water was present on the earth at the time of their formation.
this should be impossible, but rather indicates that our understanding of the planet is not as advanced as we might like to believe.
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the shell you picked up on the beach yesterday is feasibly older than you are, older than your parents and your grandparents. on an occasion far less rare than you would expect it to be, it is older than human civilization.
the dendrochronology of the clam: go to the beach. pick up a shell, then another, then a whole lot more. use their isotopic compositions to associate growth rings in one shell with growth rings in another. repeat. make a record over six thousand years long. goal: track seasonal variation year to year.
you know. hypothetically.
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insanity is repeating the same action over and over and expecting a different result.
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subduction begins when the passive margin of a continent becomes old enough for the oceanic crust their to be brittle, dense, and heavy. the connection between oceanic and continental breaks, and the oceanic crust begins to sink.
slab pull brings the rest of the plate along after it, faster than it ever was before, and the continental crust acts to scrape material off the ocean floor and preserve it in the densely folded accretionary wedge.
some material not caught initially in the wedge still is preserved on the surface. the processes are unclear, but some suggest that the pressures of the two plates grinding against each other occasionally spits something out from between them, like a watermelon seed between your lips.
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somewhere out there is the earth’s oldest ice and we don’t know if we’ve found it or not and we won’t know until there’s no ice left to be the earth’s oldest ice.
we search for the four million year consecutive record and it might be somewhere out there but we haven’t found it yet nor do we know that it exists to begin with. we haven’t found it yet, nor may we ever.
Writer | Clara Danhof ’25 | cdanhof25@amherst.edu
Editor | Venumi Gamage ’26 | vthotagodagamage26@amherst.edu