Question

The first mammal arose during the _________ period. a. Triassic b. Jurassic c. Cretaceous d. Tertiary e. Quaternary

Short answer

(a) Triassic period

Step-by-step solution

Step 1. Understand the question

This is a question regarding the history of the evolution of life on Earth. It asks in which geological period the first mammals appeared.

Step 2. Review the choices

Review each choice and consider what is known about each geological period. Triassic, Jurassic, and Cretaceous periods belong to the Mesozoic era. Tertiary and Quaternary periods are part of the Cenozoic era.

Step 3. Determine the correct answer

The first mammals appeared in the Mesozoic era, specifically during the Triassic period. Thus, the correct answer is (a) Triassic.

Key concepts

Mesozoic era

The Mesozoic Era is a significant chapter in Earth's history, spanning approximately 180 million years. This era is divided into three periods: Triassic, Jurassic, and Cretaceous. This era is well-known for its dramatic changes in life forms on Earth, particularly among animals and plants.
The Mesozoic Era is often called the "Age of Reptiles" due to the dominance of dinosaurs, but it is also crucial for the evolution of mammals. While dinosaurs roamed the land and pterosaurs flew the skies, early ancestors of birds and mammals were quietly emerging.
Mammals began to diversify, although they remained small and relatively inconspicuous throughout much of this era, in contrast to the enormous dinosaurs. The end of the Mesozoic is marked by a significant mass extinction event, which led to the decline of many species, including the dinosaurs, paving the way for mammals to flourish.

Triassic period

The Triassic period is the first period of the Mesozoic era, spanning from approximately 252 to 201 million years ago. After the Permian extinction, which was the most severe extinction event in Earth's history, the Triassic marked a gradual recovery in biodiversity.
This period is significant because it is when we first see the emergence of small mammals.
During the Triassic, life started to diversify again. Notably, the earliest known mammals evolved during this period, setting the stage for future mammalian evolution. Early mammals were quite different from the ones we know today; they were small and shrew-like, living in a world dominated by reptiles.
This period is characterized by the development of new ecosystems as the supercontinent Pangaea began to break apart. These massive geological changes influenced the climate and created new environments, promoting the evolution and diversification of life.

Geological time periods

Geological time periods are essential for understanding Earth's history. These periods are part of a larger system called the geological time scale, which segments Earth's history based on major events like mass extinctions and significant climate changes.
Each time period within the geological time scale highlights specific developments in the planet's physical characteristics and the evolution of life on Earth. The Mesozoic era, for example, is divided into three main periods: the Triassic, Jurassic, and Cretaceous. Each of these periods saw significant evolutionary leaps, such as the domination of reptiles in the Triassic and Jurassic, and the evolutionary flourishing in the Cretaceous.
Understanding these time periods helps scientists and students alike to map out the timeline of life’s history. The details of these periods provide context for how and when certain species evolved or went extinct, helping us grasp the dynamic history of our planet.