This is the third installation of my personal project to help people see sand differently and communicate the science of one of earth's most ubiquitous and fascinating materials. You can read the posts from week 1 and week 2 at these links or on my instagram.
Part 1: Sediment-Bound Nutrients.
In this photo of the Amazon river, an invisible payload goes unseen among those billowing plumes of sediment: these milky waters also carry a precious cargo that was stripped from rocks of the Andes Mountains and is now fertilizing the Amazon Rainforest.
What these life-giving nutrients are, and how their creation is tied up in the creation of sediments, is the story I want to tell with this week's installation of Sand Month.
In the past posts we have talked mostly about clastic sediments, the fragments that result from the crushing and cracking of larger rocks. These are pretty straightforward: they are essentially miniature versions of their parent rock, and the processes that yield them generally occur on a visible scale. But, they are only one part of the picture.
Alongside and behind the scenes of that physical weathering is chemical weathering: the reactions caused by the acid that CO2 forms in water. This acid eats away at rock and pulls atoms from their crystal lattice, helping weaken the rock and creating its own suite of products along the way.
The atoms that are stripped away behave like table salt, dissolving in the water to become ions in solution. Thus water accumulates a trove of rock in liquid form, aqueous minerals carted along invisibly alongside their still-solid clastic cousins.
(side note: the parent rocks are transformed as well, as atoms are plucked from their minerals they leave an altered compound in their wake: once-rigid crystals rearrange into sheets of sticky plate-like structures that combine with water to form a slick, squishy earth. We call this new compound “clay.”)
The dissolved minerals being carted away will be familiar to you-- things like potassium, calcium, sodium, phosphorous, iron, and zinc. This list reads like a nutrition label, because it is: these are essential nutrients that sustain life on earth. When your parents extol vitamins and minerals, it’s these that they mean-- their liberation from rock via chemical weathering is the leap they must make before being taken up by the food web, and eventually, you.
The upshot of this is that the process of creating sediment is also the process of fertilizing life on earth. Indeed, the sediment itself is the most productive source for these nutrients- its immense surface area and long exposure to water gives ample opportunity for water's acids to do their work.
That is why this photo of the milky sediment-rich waters of the Amazon contains so much more than meets the eye- these sediments brought down from the Andes provide the vast majority of mineral nutrients that the Amazon floodplain receives and enable the biological spectacle that exists there today.
This process is on spectacular display in the Amazon, but it occurs everywhere on earth. The richness of life on this planet would simply not be possible without the creation of sand.
If you want to learn more about the impact of sediments and their nutrients on the Amazon basin, I wrote a whole article about it for Massive Science last year. You can check it out here!
Also, this week's posts aren't quite as linear of a story as last week's on The Journey, so I'll be releasing them one at a time over the course of this week. The next post is about one of my favorite subjects of all time, the carbonate cycle.
I'll also be experimenting with some super brief video summaries of these subjects via TikTok/Instagram Reels, so you can check those out on my instagram profile if you're interested!