Adaptations L2S3

​3. Increases in the Diversity of Life

​ What comes after the soft-bodied animals that represent Earth’s earliest known multicellular organisms? The next thing that you see in the fossil record is remarkable—a sudden huge increase in the diversity of life. There are fossils of starfish, shelled animals such as mollusks, crablike crustaceans, and even an ancestor of the vertebrates. What happened on Earth at this time?

​ Many different kinds of organisms live on Earth. The term biodiversity describes the variety of species on Earth. At certain times in Earth’s history, scientists have observed a sudden, rapid increase in biodiversity. This is known as an adaptive radiation—“adaptive” because the new species are well suited to living in their environments and “radiation” because many species appear quickly, as if spreading out from a single point. One important adaptive radiation took place during the Cambrian Period about 540 million years ago, soon after multicellular life first appeared. This adaptive radiation is called the Cambrian Explosion. Rock strata from the time of the Cambrian Explosion provide fossil evidence of the origin of most of the major groups of animals found on Earth today.

Open Ended

What does the term biodiversity describe?

Open Ended

What does the word adaptive refer to?

Open Ended

What is adaptive radiation?

​At times in Earth’s history, biodiversity on Earth increased suddenly. One example of this was during the Cambrian Explosion. In this photo, scientists are excavating fossils from the time of the Cambrian Explosion.

​ What could explain this sudden increase in biodiversity? The Cambrian Explosion most likely resulted from a combination of factors. First, changes in the oceans made more habitats available at that time. Second, increasing oxygen levels in the atmosphere may have allowed for more active, complex organisms to live. Finally, key features of living things themselves may have contributed to the explosion. Some scientists think that animals first developed vision, the ability to see, at this time. Another possibility is that shells or other hard body parts originated at this time.

​What happened after the Cambrian Explosion? Did biodiversity continue to increase? Sometimes biodiversity did increase, and sometimes other adaptive radiations occurred. But a completely different pattern can also be seen in the fossil record—periods of time when many living things suddenly disappeared.

​Many different kinds of animals appeared for the first time during the Cambrian Period. The drawings show a few of the many Cambrian fossils that have been discovered.

​Answer Question in TCI Adaptations

Lesson 2 Section 3

​Must use race on all questions