Today’s Wonder of the Day was inspired by Ruby from Bloomington, IL. Ruby Wonders, “What is phytoplankton?” Thanks for WONDERing with us, Ruby!

Have you ever gone swimming in the ocean? How about in a lake or pond? Swimming in a natural body of water can open your eyes to how many things live in oceans and lakes. And you can’t even see many of them! In fact, you’d need a microscope to see organisms like plankton.

What are plankton? They’re tiny organisms that live in the Earth’s waters. There are many types of plankton, and they exist in both saltwater and freshwater. All plankton fall into one of two groups. Some of them are zooplankton, which belong in the animal kingdom. Others are phytoplankton.

Phytoplankton are plants. Like other plant life, they’re capable of photosynthesis. For that reason, these life forms live in the upper level of bodies of water. This gives them the sunlight they need to grow.

The name for plankton comes from the Greek word “planktos.” It means “drifter”—which definitely describes these tiny organisms. Plankton, including phytoplankton, rely on currents. They don’t swim with fins or tentacles. Instead, they drift from place to place with the movement of the water they live in.

How long have phytoplankton existed? They’ve been around for quite a while! Scientists trace the earliest phytoplankton species back at least 2.4 billion years. In fact, many experts believe these tiny life forms led to much of life on Earth today.

Before phytoplankton existed, the Earth’s atmosphere held very little free oxygen. That means the air wasn’t breathable. When phytoplankton came along, they began taking in huge amounts of carbon—and releasing oxygen. This is part of the process of photosynthesis. 

Over time, this led to more oxygen in Earth’s atmosphere. That led to life on dry land—including human beings. Without this initial buildup of oxygen caused by phytoplankton, much of life on Earth today may never have existed.

As you might expect, these tiny organisms  are still important to life today. In fact, scientists say that despite their small size, phytoplankton supply about half the oxygen in the atmosphere. That’s equal to the amount of oxygen produced by all the plants on dry land combined. Phytoplankton also curb climate change by removing a large amount of carbon from the air.

These life forms are also important to the biodiversity of the planet’s oceans and lakes. They are a food source for other marine life. For their small stature, phytoplankton have a huge impact on the Earth!

Of course, too much of a good thing can have a negative impact. When phytoplankton populations grow too large, they can be harmful to people and animals. They can create red tides and algal blooms that kill off marine life. They can also hurt people and other animals that eat contaminated seafood.

Phytoplankton are just one example of the delicate balance of life on Earth. If their population fell too low, it would affect the oxygen available in the atmosphere. Too large? They can have a drastic effect on other forms of life. What can you do to help protect all of Earth’s life forms?


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Join us tomorrow when we’ll learn about a religious holiday that’s celebrated by millions of people around the world!