Chapter 21: The Origin and Evolutionary History of Life

chemical evolution

During ________, small organic molecules formed spontaneously and accumulated.

Prokaryotic heterotrophs

The first cells were ________ that obtained organic molecules from the environment.

Natural selection

________ at the molecular level eventually resulted in the information sequence DNA → RNA → protein.

Mesozoic era

The ________ began about 252 mya and lasted some 186 million years.

Paleozoic era

During the ________, which began about 541 mya and lasted approximately 289 million years, all major groups of plants, except flowering plants, and all animal phyla appeared.

Cenozoic era

In the ________, which extends from 66 mya to the present, flowering plants, birds, insects, and mammals diversified greatly.

Human ancestors

________ appeared in Africa during the Late Miocene and Early Pliocene epochs.

RNA

According to a model known as the ________ world, ________ was the first informational molecule to evolve in the progression toward a self- sustaining, self- reproducing cell.

Cells

________ arose from the protobionts.

large extraterrestrial body

A collision of a(n) ________ with Earth may have resulted in dramatic climate changes that played a role in this mass extinction.

Ediacaran fauna

________ were small, soft- bodied invertebrates.

photosynthesis

The evolution of oxygen- generating ________ ultimately changed early life.

iron sulfur world hypothesis

The ________ suggests that organic molecules were produced at hydrothermal vents, cracks in the deep- ocean floor.

autotrophs organisms

Later, ________ that produce their own organic molecules by photosynthesis- evolved.

Macromolecular assemblages

________ called protobionts formed from macromolecules.

Prebiotic soup hypothesis

The ________ proposes that organic molecules formed near Earths surface in a "sea of organic soup "or on rock or clay surfaces.

Ediacaran period

The ________, from 635 mya to 541 mya, is the last period of the Proterozoic eon.

Ediacaran fossils are the oldest known fossils of mul

ticellular animals