Lesson 10: Earth’s Atmosphere Modified From: arth.ppt#264,2,Age%20of%20the%20Earth #293,13,Experimental Research on the Origin of Life U%20THINK%20EARLY%20EARTH%20WAS%20LIKEhttp://outreach.mcb.harvard.edu/teachers/Summer06/BethMick/HistoryofLife.ppt#257,6,WHAT%20DO%20YO U%20THINK%20EARLY%20EARTH%20WAS%20LIKE? of the atmosphere

WHAT WAS THE EARLY EARTH WAS LIKE? HOW OLD IS THE EARTH? 4.5 BILLION YEARS OLD METEORS FOR MILLIONS OF YEARS - HOW HOT WOULD THE EARTH BE? Earth has to Cool Down – Steam escapes and rain allows collection of water - Earth now has… –atmosphere of Ammonia, Methane, Water Vapor, CO 2, and Nitrogen –WHAT IS MISSING? Oxygen

Origin of the atmosphere Earth’s original atmosphere –Probably made up of hydrogen and helium. –These are fairly common in the universe. Original atmosphere stripped away by the solar wind –H and He are very light Hydrogen and helium have the smallest atoms by mass. –The early earth was not protected by a magnetic field. –Thus the current atmosphere is secondary

The secondary atmosphere Formed from degassing of volcanoes Gasses emitted probably similar to the gasses emitted by volcanoes today. –H 2 O (water), 50-60% –CO 2 (carbon dioxide), 24% –SO 2 (sulfur dioxide), 13% –CO (carbon monoxide), –S 2 (sulfur), –Cl 2 (chlorine), –N 2 (nitrogen), –H 2 (hydrogen), –NH 3 (ammonia) and –CH 4 (methane)

Earth’s Modern atmosphere Nitrogen (N2)- 78%, Oxygen (O2)- 21%, Carbon Dioxide (CO2) 0.03 %, Where did all the oxygen come from?

In the Sea (1): Bombardment million years ago NASA © Julian Baum with permission Early Earth During its early history, the Earth was bombarded by meteorites. Such inhospitable conditions probably prevented life from evolving.

In the Sea (2): First living things million years ago en.wikipedia.org/wiki/Image:Stromatolites_in_Sharkbay.jpg Modern bacterial mounds Fossil bacteria? Life evolved shortly after the bombardment ended, early in Earth History. The first living things were simple bacteria

First Living Things: Bacteria The first living things were simple forms of life, anaerobic bacteria, may have formed more than 3.6 billion years ago (only 1 billion years after Earth was created). These life forms, also called cyanobacteria or “blue- green algae”, did not require oxygen to breathe (as do nearly all organisms inhabiting Earth at the present time).

In the Sea (3): Oxygen million years ago Iron oxide rocks Early photosynthetic bacteria produced oxygen and released it as a waste product. This added oxygen to the atmosphere for the first time. Photosynthetic bacteria en.wikipedia.org/wiki/Image:Anabaena_sperica.jpg

Oxygen in the Atmosphere! Anaerobic, photosynthetic bacteria converted atmospheric carbon dioxide (CO 2 ) into oxygen (O 2 ) and carbohydrates. This made the evolution of more complex life forms possible, including all animal life, that breathe oxygen and feed upon plant carbohydrates.

In the Sea (4): Complex cells 1900 million years ago Two billion years later complex eukaryote cells appeared. These had compartments with special functions such as energy factories called mitochondria. Eukaryote cells need oxygen - this explains their late evolution

In the Sea (5): Multicellular life 1400 million years ago After another half billion years many-celled life appeared Grypania was a coiled tube, 2 mm wide and up to 5 cm long Grypania © Bruce Runnegar with permission

Evolution of Oxygen Content of Earth’s Atmosphere