Zaman Ais: Pengenalan dan Terminologi

• The Ice Age, or more accurately, glacial periods within an Ice Age, refers to periods in Earth's history when ice sheets covered large portions of the globe.
• The most recent glacial period peaked around 20,000 years ago, marking the end of the Pleistocene Epoch.

Definition and Terminology

• Ice Age: A long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers.
• Glacial Period (or Glacial): A period within an Ice Age when ice sheets advance.
• Interglacial Period: A period within an Ice Age when ice sheets retreat.
• Stadial: A period of significant cooling within a glacial period.
• Interstadial: A warmer period within a glacial period.

Major Ice Ages in Earth's History

• Huronian Glaciation: The oldest known Ice Age, occurring in the Paleoproterozoic Era (2.4–2.1 billion years ago). Possibly caused by the Great Oxidation Event.
• Cryogenian Period: A period in the Neoproterozoic Era (850–630 million years ago) characterized by extreme glaciation, possibly covering the entire planet (Snowball Earth).
• Andean-Saharan Glaciation: Occurred in the late Ordovician period (460–430 million years ago).
• Karoo Ice Age: Occurred in the Pennsylvanian and Permian periods (360–260 million years ago), affecting Gondwana.
• Quaternary Glaciation: The most recent Ice Age, starting about 2.58 million years ago and continuing to the present. It includes the Pleistocene and Holocene epochs.

The Quaternary Glaciation

• Characterized by cycles of glacial and interglacial periods.
• Pleistocene Epoch: Marked by repeated glacial advances and retreats.
• Holocene Epoch: The current interglacial period, which began about 11,700 years ago after the last glacial period.

Causes of Ice Ages

• Milankovitch Cycles: Changes in the Earth's orbit and tilt affect the amount and distribution of solar radiation. These cycles include:
  • Eccentricity: Changes in the shape of Earth's orbit around the Sun.
  • Obliquity: Changes in the tilt of Earth's axis.
  • Precession: Wobble of Earth's axis.
• Atmospheric Composition: Changes in greenhouse gas concentrations, such as carbon dioxide and methane, can significantly impact global temperatures.
• Plate Tectonics: The movement of continents can affect ocean currents and atmospheric circulation, influencing climate patterns.
• Solar Activity: Variations in the Sun's energy output can play a role in climate fluctuations.
• Volcanic Activity: Large volcanic eruptions can release aerosols into the atmosphere, which can temporarily cool the planet.

Effects of Glaciation

• Landscape Changes: Glaciers erode and deposit sediment, creating distinctive landforms such as:
  • U-shaped valleys
  • Cirques
  • Aretes
  • Moraines
  • Eskers
  • Kames
• Sea Level Changes: During glacial periods, water is stored in ice sheets, causing sea levels to drop. During interglacial periods, melting ice sheets cause sea levels to rise.
• Isostatic Rebound: The weight of ice sheets depresses the Earth's crust. When the ice melts, the land gradually rises back up (isostatic rebound).
• Changes in River Systems: Glaciation can alter river courses and create new drainage patterns.
• Lake Formation: Glacial erosion and deposition can create lakes, such as the Great Lakes in North America.
• Faunal and Floral Shifts: Climate changes associated with glacial periods cause shifts in the distribution of plant and animal species.

Evidence of Past Glaciation

• Glacial Striations: Scratches on bedrock caused by rocks embedded in moving ice.
• Till Deposits: Unsorted sediment deposited by glaciers.
• Erratics: Large rocks transported by glaciers and deposited far from their origin.
• Moraines: Ridges of sediment deposited at the edges of glaciers.
• Eskers: Winding ridges of sand and gravel deposited by meltwater streams flowing under glaciers.
• Kettle Lakes: Depressions left by melting blocks of ice.
• Pollen Records: Analysis of pollen grains in sediment layers can reveal changes in vegetation and climate.
• Oxygen Isotopes: The ratio of oxygen-18 to oxygen-16 in ice cores and marine sediments can provide information about past temperatures.

The Last Glacial Maximum (LGM)

• The most recent glacial period peaked around 20,000 years ago.
• Ice sheets covered much of North America, Europe, and Asia.
• Sea levels were about 120 meters lower than today.
• Global temperatures were significantly colder than today.

The Younger Dryas

• A brief return to glacial conditions that occurred about 12,900 to 11,700 years ago, during the transition from the last glacial period to the Holocene.
• Possible causes include changes in ocean circulation.

The Holocene Epoch

• The current interglacial period, which began about 11,700 years ago.
• Characterized by relatively stable climate conditions.
• Human civilization developed and flourished during this epoch.

Future Ice Ages

• Milankovitch cycles suggest that the Earth is likely to enter another glacial period in the future.
• However, the timing and severity of future glaciations may be affected by human-caused climate change.