Early Life Forms and Their Adaptations — Passage and Quiz

Long ago, Earth looked very different than it does today. If we could travel back 500 million years, we would find most life living in the oceans. There were no trees, no flowers, and no animals walking on land yet!

These ancient oceans were filled with strange creatures. Some had hard shells to protect their soft bodies. Others had special eyes that could spot danger. Many had ways to move quickly through the water to escape from predators.

One of the most common animals was the trilobite. Trilobites had hard outer shells like armor. These shells protected them from animals that wanted to eat them. They also had many legs to help them crawl along the ocean floor. Their special eyes could see in many directions at once, helping them spot danger.

Not all early animals had hard shells. Some were soft like jellyfish. These animals had stinging cells that would hurt any creature that tried to eat them. Others could quickly change direction when swimming to escape from larger animals.

Many of these early creatures don't exist anymore. They became extinct when their environment changed and they couldn't adapt. Others evolved—changed slowly over time—into different animals. For example, some animals with simple backbones eventually gave rise to fish, and much later, to all animals with backbones including humans!

Scientists learn about these ancient animals by studying fossils—the remains or imprints of organisms preserved in rock. Fossils show us that all living things have special features, or adaptations, that help them survive. Animals with useful adaptations were more likely to live long enough to have babies. They passed these helpful features to their offspring.

This is why we see such amazing diversity in living things, both long ago and today. Each creature has its own special set of adaptations that helps it live in its particular environment. Yet all living things share a connection—they are part of Earth's great family tree of life.