|Source: National Geographic|
- How is it that a one-time collection of cosmic dust has gradually changed over time and produced this incredible planet with its tremendous biological diversity?
- What transitions has Earth gone through and why?
- How does evidence of the deep past inform us about today’s conditions?
- How does the Earth’s geological carbon cycle act as a thermostat?
Over the course of Earth's existence she has gone through a lot of changes and continues to change today as she grapples with pollutants in her water, increased carbon dioxide in her atmosphere, and habitat destruction on land. Earth has moved from a red-hot, toxic, uninhabitable planet 4.6 billion years ago to the amazing, beautiful, diversified planet on which we now live. Fossil and geologic records provide a trail for us to follow to understand Earth's ancient past. Earth has redesigned and redefined herself many times. She started out a red-hot, boiling sea of molten rock-- a magma ocean formed by whirlwind collisions of space rock that transferred both matter and thermal energy between atoms and molecules. She cooled, crusted over, and let steam off to condense into clouds and rain, further cooling her surface. More clouds formed and storms raged, covering Earth with water. Water, our life-giving substance.
The oceans formed and Earth became a blue planet. Or mostly blue because she kept some rock exposed and resting on plates that moved with the internal workings of her still molten mantle. The tectonic plates have been traveling around Earth's oceans 3.9 billion years, carrying with them evidence of their movements and the life they have seen.
Planet Earth has had an eventful history of climate changes -- warm periods and ice ages -- and species evolutions and extinctions. Lives lived on the planet are documented in Earth's diary of fossil records. By reading Earth's geologic diary we can learn how she adjusts, how the atmosphere responds to certain conditions, how Earth uses and recycles carbon dioxide to regulate her surface temperature. Earth leaves us this history in rock, readable through close examination and radiometric dating, so we may better understand her temperament.
This is just all to say that Earth is sensitive, and we can get perturbations that can lead to a different world. ~ Francis Macdonald, quoted by Dell'Amore, Christine. "Snowball Earth" Confirmed: Ice Covered Equator."National Geographic. National Geographic Society, 04 Mar. 2010. Web. 31 July 2014.