The Evolution of Life on Earth

The Evolution of Life on Earth

A million years ago, the most significant event on Earth occurred- life emerged. Originating from single-celled organisms, they became complex, specialized beings. Miraculously, several million years later, an incredible collection of jawed, clawed, and conscious animals evolved.

Every adaptation in the world is a result of natural selection. If an animal’s natural habitat disappears, it’s forced to either accommodate for its surroundings or perish. This evolution allows for the development of new species, as well as the extinction of old ones.

Between incomplete fossil records and DNA tracking, the history of life on Earth is tricky to pin down. Although modern genetics make the process simpler, specific dates are still quite uncertain due to confounding factors. Therefore, they should be taken as approximate.

Experts guess that the beginning of life on Earth originated 3.8 billion years ago. These organisms developed in undersea alkaline vents. Although the process is uncertain, at some point back in time, one lineage “gave birth” to two main life forms- bacteria and archaea.

About 2 billion years later, oxygen was released into the atmosphere. A little later, Eukaryotic cells- cells with organelles- come into existence. These cells split into three groups; the ancestors of modern plants, fungi, and animals. At the time, they were still single-celled organisms. It is unknown in which order the groups broke apart.

The first multicellular organisms developed approximately one billion years ago. Sometime later, they divided into two categories- sponges and Eumetazoa. 200-million years later, a group called placozoa breaks away from the rest of Eumetazoa. Many believe that placozoa is the last common ancestor of all animals.

Moving forward, 630 million years ago, some animals evolved to have bilateral symmetry- they had a distinct top, bottom, front, and back. As to how this happened, little is known. A bit later, the first fossil evidence of animals exploring land arose. The first animals to do so were presumably the euthycarcinoids. Before this time, all creatures lived in water. Not long after, The Great Ordovician Biodiversification Events began, causing an increase in diversity.

Fast-forwarding, the late ancestors of primates split from the rodents and lagomorphs. Through eons of natural selection, humans evolved. They belong to a sub-category of primates known as The Great Apes.