Many dramatic changes to the Earth’s climate have occurred over the planet’s 4.5-billion-year history. Long periods of stability, or equilibrium, are occasionally disrupted by periods of change that vary in length and intensity. Climatic shifts are destructive, and some even caused mass extinction events that wiped out high percentages of species. Despite these extinctions, life has always rebounded, allowing new species to dominate the landscape.
770 million years ago - Snowball Earth
Scientists believe that there may have been several times when the entire Earth was frozen over with ice. There is no consensus as to what exactly caused these frigid events. One theory holds that a number of large volcanic eruptions sent sulfur gas particles into the atmosphere that reacted with solar radiation to produce a cooling effect. Some scientists speculate that snowball conditions facilitated an explosion of multicellular organisms.
305 million years ago - Carboniferous Rainforest Collapse
The Carboniferous period was known for its marshy forest communities inhabited by the ancestors of reptiles, mammals, and amphibians. It was also an “icehouse” period, in which permanent ice caps sat at the Earth’s poles. But around 305 million years ago, levels of carbon dioxide, a greenhouse gas, increased. Greenhouse gasses prevent heat from escaping the atmosphere into space, insulating the Earth. This caused the planet to warm, dry out, and experience more intense seasonal fluctuations. Such a climate was intolerable for the Carboniferous rainforest plants, leading to a shift in the types of plant and animal communities and eventually the age of the dinosaurs.
66 million years ago - Cretaceous-Paleogene extinction event
The most well-known example of extreme climate change is the Cretaceous-Paleogene extinction event, the extinction of the dinosaurs. 66 million years ago, an asteroid collided with the Earth, sending a colossal cloud of ash and other debris into the atmosphere. This dense cloud blocked out the sun, creating an “impact winter” and halting the photosynthesis of plants and phytoplankton. The effects of the impact winter rippled throughout ecosystems, causing the extinction of the non-bird dinosaurs.
55 million years ago – Permian-Eocene Thermal Maximum
Over a period of about 100,000 years, the planet slowly warmed by between 5° and 8° Celsius (9°-14.4° Fahrenheit). What caused the warming? Some scientists point to a volcanic eruption that prompted marine sediments to release the powerful greenhouse gas methane into the atmosphere. Oceans across the globe reached tropical temperatures, causing the extinction of a significant percentage of marine life.
18,000 years ago – Glaciers begin to retreat and our modern landscape is revealed
There have been at least five major "ice ages" or glacial periods in Earth's history. Scientists note that these cycles correspond to small shifts in the Earth's orbit around the sun. During glacial periods, ice caps form at the north and south poles, and glaciers cover large areas of land. The most recent ice age is known as the "Quaternary glaciation" or "pleistecene glaciation." This glaciation is actually still ongoing today, although we are currently experiencing an "interglacial" period. About 18,000 years ago, glaciers (that once reached as far south as Illinois in North America) began retreating, revealing the modern landscape we know today. The Chesapeake Bay is one of the waterways formed by the melting of glaciers.
What do these dramatic shifts in Earth’s climate have in common?
In these examples, we saw that geological phenomena and natural cycles can drastically alter the Earth's physical attributes. This includes the chemical composition of Earth’s oceans and atmosphere, the wind and ocean currents, the ice caps, and other factors that contribute to Earth's climate. These shifts in climate – rainfall, temperature, sea level, and more – can in turn alter entire landscapes and severely disrupt the ability of organisms and ecosystems to function.
Last updated: August 28, 2023