The ginormous collision that tilted our planet - Elise Cutts

Key Concepts:

• Big Whack: A collision between early Earth and a Mars-sized object.
• Axial Tilt (Obliquity): The angle of Earth's rotational axis relative to its orbital plane (currently ~23.5°).
• Seasons: Annual cycle of climate changes caused by Earth's axial tilt.
• Climate Cycles: Long-term variations in Earth's climate influenced by changes in axial tilt.
• Ice Ages: Periods of extensive glaciation on Earth.
• Glacial Period: A phase within an ice age characterized by advancing ice sheets.

1. The Big Whack and Earth's Tilt:

• 4. 5 billion years ago, a Mars-sized object struck the early Earth at approximately nine kilometers per second.
• This collision, known as the "Big Whack," vaporized portions of both bodies and created a molten magma ocean on Earth's surface.
• The Big Whack is responsible for the formation of the Moon from the debris.
• The collision also knocked Earth off-kilter, resulting in its axial tilt.

2. Earth's Axial Tilt (Obliquity):

• Earth spins around an axis that runs between the planet's poles, completing one rotation per day.
• The Earth's axis is tilted at approximately 23.5 degrees relative to its orbital plane. This tilt is called axial tilt or obliquity.
• The Moon's gravitational pull largely stabilizes Earth's axial tilt.

3. The Impact of Obliquity on Seasons:

• Obliquity is the primary reason for Earth's seasons.
• When sunlight hits a surface head-on, it is concentrated. When it hits at an angle, it is spread out.
• As Earth orbits the Sun, the Northern Hemisphere angles towards the Sun for part of the year, resulting in summer due to more direct sunlight.
• Half a year later, the Northern Hemisphere angles away from the Sun, causing winter with longer shadows and colder temperatures.

4. Obliquity and Climate Cycles:

• Changes in Earth's axial tilt impact the planet's climate.
• Earth's axial tilt wobbles between 24.5° and 22.1° every 41,000 years.
• Higher axial tilt leads to more extreme seasons and less climate variation with latitude.
• Lower axial tilt results in milder seasons and more extreme climate variations.
• Decreasing axial tilt causes milder polar summers, allowing ice to accumulate and potentially trigger a glacial period.
• The freeze and thaw cycles of Earth's Ice Ages historically aligned with the 41,000-year rhythm of axial tilt changes.
• Over the past million years, changes to ice sheets in the Northern Hemisphere have extended these ice age cycles.

5. Consequences of No Axial Tilt:

• If Earth lost its axial tilt entirely, there would be no seasons.
• The tropics would receive direct sunlight year-round, while the poles would receive only glancing rays.
• One speculative scenario suggests that the lack of summer melt could cause ice sheets to grow continuously, reflecting more sunlight and cooling the Earth.
• This could potentially lead to a "snowball Earth" scenario, where the entire planet is encased in ice.
• Earth's tilt is involved in so many planetary processes that it’s impossible to say precisely what Earth would look like without it.

6. Conclusion:

• Earth's axial tilt and the seasons it creates are essential for maintaining the planet in a state suitable for life.
• The Big Whack, a cosmic collision in Earth's early history, inadvertently set the stage for the planet's current conditions.