Paleoclimatology

  • Paleontology - the study of ancient, pre-historic life.
  • Paleoclimatology - the study of ancient, pre-historic climate.
See "My how you've changed!" - Smithsonian site about the history of Earth's atmosphere.

Icehouse Earth and Greenhouse Earth

Some questions for you to look into about Earth's paleoclimate...Scientists claim that Earth's climate has varied between icehouse and greenhouse conditions.

  1. What distinguishes icehouse and greenhouse climate states?
  2. Based on the definitions, which one are we in now?
  3. About what percentage of Earth's geologic history has been in the icehouse state? in the greenhouse state?
  4. What are some factors that are thought to cause Earth to switch from one to the other?
  5. Is what we call "the Ice Age" the same as the icehouse state? and now that we're out of the ice age are we in a greenhouse state?

Earliest Earth

What do we know about the vast expanse of Earth's history?

  • Earth is approximately 4.6 billion (4,600 million) years old.
  • By the start of the Archean eon 4-2.5 billion years ago (YA)--1/3 of Earth's history! -- Earth's crust cooled enough for rocks to form.
    • Nitrogen ~ the same as today
    • Practically no Oxygen.
    • $CO_2$ 10-2500 times today.
    • $CH_4$ (methane) 100-10,000 times today.
    • Sun dimmer: ~70% of today.
  • 2.5-1.9 billion YA, photosynthetic cyanobacteria were responsible for The Great Oxygenation Event: Atmospheric $O_2$ rises from less than 1 ppm ($10^{-4}$%) to about ~2%. Atmospheric carbon switched from predominantly $CH_4$ to predominantly $CO_2$.

    Red: highest estimate of $O_2$
    Green: lowest estimate of $O_2$
  • Cambrian 541 million YA - first animals in the ocean.
  • Ordovician - first land plants (471 million years ago), mosses and liverworts (non-vascular plants), plunged Earth into an ice age as $RCO_2$ dropped from 22$\to$8.
  • Devonian era 419 million YA - Free sporing vascular land plants develop, and mark the beginning of plant spread on land, forming vast forests.

    All the continents were below the equator!
  • Age of the dinosaurs, started about 245 million YA. End of the dinosaurs: 65 million YA a massive asteroid strike leaves the Chicxulub crater.

Temperatures and $CO_2$ over the last 540 million years

"$RCO_2$" means ratio of $CO_2$ levels to pre-industrial (~300 ppm).
$RCO_2=20$ means "20 times as much $CO_2$ as pre-industrial.
$RCO_2=416/300 = 1.4$ today (2019).

(Berner, Science, 1997)

See Earth's Climate System, Salawitch, et. al (2017), who produced this graph:

Glen Fergus, WikiMedia Commons

Temperature, Sea level, and $CO_2$ in just the last 400,000 years

[Use the OpenSeadragonizer browser extension to explore this poster.]