Born of Ice and Fire: How Glaciers and Volcanoes (with a Pinch of Salt) Drove Animal Evolution

The Cryogenian Period, when our planet was covered in ice for millions of years, led to the remarkable biodiversity known as the Cambrian explosion. Graham Shields explores how inhospitable conditions enabled animals to evolve, radiate, and diversify into our earliest ancestors, navigating the wild swings between hot and cold climates, oxygenation and asphyxiation, biological radiations, and extinctions. He guides readers through evidence found in the Australian outback, Mongolia, Scotland, and other locales, revealing how geologists can trace glaciation, the atmosphere, oceans, mountain building, and more through the earth's rocks.

Format: Hardback
Length: 352 pages
Publication date: 09 January 2024
Publisher: Yale University Press

More than half a billion years ago, our world was completely covered by glaciers, a "Snowball Earth" that persisted for millions of years. Incredibly, this unimaginable cold led to the remarkable diversification of life on earth known as the Cambrian explosion. With a geologist's eye and a knack for storytelling, Graham Shields explores when and how such inhospitable conditions enabled animals to evolve, radiate, and diversify into our earliest ancestors.

This journey navigates the wild swings between hot and cold climates, oxygenation and asphyxiation, biological radiations and extinctions, asking how such instability relates to grander forces that brought our planet to its modern state. Shields guides readers through evidence found in the Australian outback, Mongolia, Scotland, and other locales, revealing how geologists can trace glaciation, the atmosphere, oceans, mountain building, and more through the earth's rocks, providing a comprehensive theory of how life evolved and diversified.

The Snowball Earth hypothesis suggests that our planet was completely covered in ice for millions of years, with temperatures dropping as low as -20°C. This extreme cold led to the formation of glaciers, which spread across the entire surface of the planet. The ice age lasted for approximately 70 million years, from around 600 million to 530 million years ago.

During this period, the Earth's atmosphere was very different from what we see today. There was no free oxygen in the air, and most organisms were anaerobic, meaning they could survive without oxygen. This led to the development of new respiratory systems, such as the ability to breathe through the skin or through specialized organs.

The ice age also had a significant impact on the Earth's geology. The glaciers carved out deep valleys, mountains, and other features that we see today. They also deposited large amounts of sediment, which formed sedimentary rocks such as limestone and shale.

One of the most significant events during the Snowball Earth period was the emergence of life on Earth. The first organisms to appear were small, single-celled bacteria. These bacteria were able to survive in the harsh conditions of the ice age by forming colonies and producing organic compounds that could absorb carbon dioxide from the atmosphere.

Over time, these bacteria evolved into more complex organisms, such as algae and protozoa. These organisms were able to photosynthesize, meaning they could produce their own food through the process of converting sunlight into energy. This allowed them to grow and diversify into a wide range of species.

Another important event during the Snowball Earth period was the development of the oxygenation of the Earth's atmosphere. Around 540 million years ago, the amount of oxygen in the atmosphere began to increase, leading to the emergence of multicellular organisms. These organisms were able to breathe oxygen, which allowed them to grow and evolve more rapidly than their anaerobic predecessors.

The Snowball Earth period also saw the development of the first animals. The first animals to appear were simple creatures, such as sponges and jellyfish. These animals were able to survive in the harsh conditions of the ice age by forming colonies and filtering out food from the water.

Over time, these animals evolved into more complex organisms, such as fish, reptiles, and mammals. These animals were able to adapt to a wide range of environments, from the ocean to the land. They also developed a range of adaptations, such as fins, scales, and fur, that helped them survive in their respective habitats.

The Snowball Earth period ended around 530 million years ago, when the Earth's atmosphere began to warm up. This warming was caused by a combination of factors, including the release of greenhouse gases from the Earth's interior and the melting of the ice caps. The melting of the ice caps led to the formation of the ocean, which increased the amount of heat that was absorbed by the Earth's surface.

The end of the ice age also led to the diversification of life on Earth. As the atmosphere became more oxygenated, new species of plants and animals were able to emerge. These species were able to adapt to the changing environment and compete with each other for resources.

The Snowball Earth period was a critical period in the history of life on Earth. It led to the development of new respiratory systems, the emergence of life, the development of the oxygenation of the atmosphere, and the diversification of life. The period also had a significant impact on the Earth's geology, which we still see today.

In conclusion, the Snowball Earth period was a period of extreme cold and ice that lasted for millions of years. It led to the remarkable diversification of life on Earth, including the emergence of new respiratory systems, the emergence of life, the development of the oxygenation of the atmosphere, and the diversification of life. The period also had a significant impact on the Earth's geology, which we still see today.

Dimension: 216 x 140 (mm)
ISBN-13: 9780300242591