Chapter 3B Main Ideas

1. Overview of Earth’s Climate History

Earth’s climate has fluctuated between cold icehouse conditions and warm greenhouse conditions throughout its history. Climate is mostly in greenhouse conditions throughout Earth’s history with the Early Cenozoic Era (during the Early Paleogene Period) being a particularly warm time period with the Paleocene-Eocene Thermal Maximum and the Early Eocene Climatic Optimum. There have been 5 major icehouses, or ice ages: the Huronian, Cryogenian, Early Paleozoic, Late Paleozoic, and Late Cenozoic Ice Ages.

2. Pre-Cenozoic Ice Ages

The Huronian is the oldest ice age and likely triggered by the onset of oxygenic photosynthesis and the Great Oxidation Event. The Cryogenian Ice Age is also commonly called the “Snowball Earth” as glacial ice extended into equatorial latitudes. This was triggered by the rifting of the supercontinent Rodinia. The Late Paleozoic Ice Age was triggered by increased photosynthesis and the formation of the supercontinent Pangea.

3. Early Paleogene Greenhouse

The Early Paleogene Period (during the Paleocene and Eocene Epochs) was particularly warm with a sharp rise in temperatures during the short-lived Paleocene-Eocene Thermal Maximum. This was triggered by a massive release of carbon to the atmosphere. This led to major changes in atmospheric and ocean chemistry and ecological changes.

4. Late Cenozoic Ice Age

The Late Cenozoic Ice Age began with the growth of glaciers in Antarctica around 34 Ma followed by Northern Hemisphere glaciation beginning around 3 Ma. Onset of icehouse conditions are due to atmospheric drawdown of carbon dioxide from increased weathering as the Himalayas started forming. Changes in ocean circulation due to the opening of the Drake Passage and closing of the Isthmus of Panama further cooled conditions at the poles. Currently the planet is in an interglacial time of the Late Cenozoic Ice Age.

The Pleistocene Glaciation, popularized as just “The Ice Age”, was the time of Northern Hemisphere glaciation. Specific landscape features and animal migrations are a direct result of the Pleistocene Glaciation.

5. Measuring Past Climates

Paleoclimate is determined by using direct data and indirect, or proxy, data. Direct data are collected using instruments that record climate directly while proxy data are collected by analyzing signals in the geological or biological record. Proxy data allows scientists to understand climate in the distant past before humans began recording climate information using instruments. Oxygen isotopes are important for calculating temperatures in the past and can be analyzed from various geologic records including seafloor sediments and ice cores.