Diatom

Diatoms are a massive group of microscopic algae found in oceans, waterways, and soil.

These organisms are classified as eukaryotes, meaning they have a cell nucleus enclosed in a membrane. They are a type of phytoplankton, which is the most common form of plankton.

As part of the Earth's biomass, they play a vital role in our global ecosystem. They are responsible for generating about 20 to 50 percent of the oxygen produced on Earth each year. Additionally, they absorb over 6.7 billion tonnes of silicon from their environments annually.

In the oceans, diatoms constitute nearly half of all organic material.

The most unique feature of a diatom is its cell wall, known as a frustule. This structure is made of silica, specifically hydrated silicon dioxide.

The frustule consists of two overlapping halves: the larger epitheca and the smaller hypotheca. These halves fit together like a petri dish or a box. The cell wall is often highly patterned with ribs, pores, and spines. These intricate designs allow the frustule to produce structural coloration. This effect is so beautiful that diatoms are often called "living opals" or "jewels of the sea."

Diatoms follow a specific process to grow and reproduce. They convert light energy into chemical energy through photosynthesis, using yellowish-brown chloroplasts.

To build their shells, they synthesize biogenic silica inside their cells. They polymerize silicic acid monomers and then extrude the material to the cell exterior. When a diatom undergoes asexual multiple fission to divide, each daughter cell keeps one of the original frustule halves. The new cell then grows a smaller half inside the old one. This causes the average size of the population to decrease over time. To fix this, they eventually form an auxospore through sexual reproduction to regain their large size.

Scientists divide diatoms into two main morphological groups. The first group is centric diatoms, which are radially symmetric. These cells often have a large central vacuole filled with cell sap. The second and larger group is the pennate diatoms, which are broadly bilaterally symmetric.

Pennate diatoms can move along solid surfaces using cytoplasm that streams along slits called raphes. While most diatoms move passively with ocean currents or wind, the male gametes of centric diatoms possess flagella. This allows them to swim actively to find female gametes. Some unique species, called dinotoms, even host diatom endosymbionts inside them. These endosymbionts have lost their silica cell walls, making them the only known shell-less diatoms.

The history of diatoms stretches back millions of years. Fossil evidence suggests they originated during or before the early Jurassic period.

This was roughly 150 to 200 million years ago. The oldest known fossil specimen is an extant genus, Hemiaulus, found in Late Jurassic amber from Thailand. Today, phycology is the branch of science dedicated to studying these organisms. Scientists have documented about 12,000 species, though many more likely remain undiscovered. They use diatoms to monitor water quality and study past environmental conditions.

Diatoms have a massive impact on the physical world through their remains. When they die, their silica shells sink and become part of marine sediment.

These accumulations form diatomaceous earth, a soft, silica-rich sedimentary rock. This material is easily crumbled into a fine powder with particles between 10 and 200 micrometers. Humans use this powder for water filtration, as a mild abrasive, in cat litter, and to stabilize dynamite. Even the Amazon basin relies on them, as 27 million tons of diatom shell dust are carried from the African Sahara to fertilize the region annually.

Recent studies show that changes in the ocean can affect diatom populations. In the mixed layer of the ocean, waves and currents churn to bring nutrients to the phytoplankton.

However, a NASA study found that diatom populations declined by more than 1 percent per year between 1998 and 2012. This happened because the mixed layer became shallower, meaning fewer nutrients reached the diatoms. This decline is significant because it may reduce the amount of carbon dioxide drawn from the atmosphere. If fewer diatoms are present, less carbon is transferred to the deep ocean for long-term storage, affecting the entire global carbon cycle.