Last universal common ancestor

Imagine you and your best friend are both starting a new school. On the first day of school, you are put into different classes and meet new classmates. However, over time, you and your friend start to notice that some of your classmates have similar physical features, like hair color or eye shape.

Now imagine this happening to every living thing on Earth - plants, animals, bacteria - over millions and millions of years. Scientists believe that every living thing on Earth can be traced back to one common ancestor that lived a very long time ago. This is known as the Last Universal Common Ancestor (LUCA for short).

LUCA was a single-celled organism that existed around 3.5 to 4 billion years ago. It may have looked similar to modern-day bacteria or archaea. From LUCA, all life on Earth evolved through a process called natural selection.

While we may never know exactly what LUCA looked like or how it lived, scientists have figured out some things about it by studying the genetic material present in different living things. By looking at the similarities and differences in genetic material, scientists can create a tree of life that shows the relationships between different species and ultimately leads back to LUCA.

So next time you learn about all of the different organisms that exist on Earth, remember that they all share a common ancestor that lived a very, very long time ago!