Climate Through Earth's History — Reading Comprehension

Earth’s climate has shifted dramatically over millions of years, alternating between freezing ice ages and warm, lush periods. These natural changes in climate have shaped the evolution of life and the surface of our planet. Understanding how and why these changes happened helps scientists predict what might occur in the future. Today, researchers use evidence from many sources to reconstruct past climates and investigate the causes behind these global shifts.

Mechanisms of Natural Climate Change

Several key processes drive natural changes in climate. One major factor is volcanic eruptions, which can release huge amounts of ash and gases into the atmosphere. These particles reflect sunlight, sometimes cooling the planet for years. Another cause is asteroid impacts. When large asteroids hit Earth, they throw dust into the air and block sunlight, leading to sudden drops in temperature. Over millions of years, continental drift—the slow movement of continents—changes ocean currents and wind patterns, shifting heat around the globe. The shape of Earth’s orbit around the Sun also changes in predictable cycles, called Milankovitch cycles. These cycles affect how much sunlight different parts of Earth receive, triggering ice ages or warmer periods. Finally, the composition of the atmosphere—the mix of gases like carbon dioxide—plays a crucial role in trapping heat and influencing climate.

Evidence from Earth's Past

Scientists study the history of Earth's climate using ice cores, fossils, sediment layers, and tree rings. For example, ice cores drilled from Antarctica and Greenland show patterns of temperature and greenhouse gases over hundreds of thousands of years. Fossils reveal which plants and animals lived in certain periods, indicating whether the climate was hot or cold. Sediment layers at the bottom of oceans and lakes contain pollen, ash, and tiny organisms, providing clues about past environments. Tree rings record yearly changes in temperature and rainfall, allowing scientists to reconstruct climate over thousands of years. Together, these records show that around 20,000 years ago, during the last major ice age, thick ice sheets covered much of North America and Eurasia.

Climate Change and Life on Earth

Sudden or extreme changes in climate have caused major challenges for life. For instance, mass extinctions—like the one that wiped out the dinosaurs—are often linked to rapid climate shifts caused by asteroid impacts or massive volcanic eruptions. The largest extinction in Earth’s history, the Permian Extinction, eliminated about 90% of species, likely because of drastic climate change. While natural factors have always driven climate changes, scientists have observed that the current rate of change is much faster than in the past. This raises concerns about how quickly ecosystems and human societies can adapt.

Understanding past climate change demonstrates the importance of Earth's interconnected systems and how small changes can lead to big effects. By studying ancient climates, scientists gain insights into the processes that drive today’s changes and help predict future impacts on our environment.

Interesting Fact: The thick ice sheets from the last ice age were more than 3 kilometers (almost 2 miles) thick in some places—taller than many mountains today!

What is one main cause of natural climate change mentioned in the passage?

How do scientists study Earth's past climates?

What are Milankovitch cycles?

Which event is linked to the extinction of dinosaurs?

What does the term "atmospheric composition" mean as used in the passage?

What is a mass extinction?

Why is the current rate of climate change concerning, according to the passage?

What role do sediment layers play in climate science?

True or False: Ice cores can show scientists what the climate was like thousands of years ago.

True or False: Continental drift has no effect on Earth's climate.