Chapter 17.2: Earth’s Early History

Age of the Earth It is estimated that the Earth is 4.6 billion years old Theories of how the Earth was “born” vary (IE – the Big Bang Theory) Elements arranged themselves according to density Least dense make up the atmosphere, most dense make up the core

Earth’s Early Atmosphere Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water All toxic gases except the water

The Early Earth It wasn’t until 4 billion years ago that the first solid rocks formed It wasn’t until 3.8 billion years ago that the Earth was cool enough to have liquid water So this is when the first oceans formed

Formation of Organic Molecules Early atmosphere allowed the formation of organic molecules Did not have oxygen Would not form in today’s atmosphere Oxygen is too reactive Bacteria would eat the molecules

Miller and Urey Stanley Miller and Harold Urey attempted to answer what the Earth’s early atmosphere and how life began Filled an enclosed flask with hydrogen methane, ammonia, and water to represent the atmosphere Passed electricity through this mixture

The Results Amino acids began to form after a couple days Extensions of their experiments have also shown to make nucleotides Scientists think that these were the first steps to life

The First Cells Thought to have originated 200-300 million years after oceans formed Earliest cells called proteinoid microspheres were created when organic molecules became trapped in bubbles Not alive but have some characteristics of living cells

Oxygen-Free Life Forms The first life forms are thought to have evolved in oxygen free environments approximately 3.5 billion years ago Photosynthetic organisms evolved in the oceans approximately 2.2 billion years ago Started pumping oxygen into the atmosphere

Rusty Oceans When oxygen mixed with iron in the water, the oceans began to rust The iron oxide sank to the bottom of the oceans giving us the iron ore deposits that we use today

The Ozone Layer The ozone layer formed when oxygen began to accumulate in the atmosphere Created a poisonous atmosphere where most of the organisms became extinct Those that survived became the anaerobic organisms that we know today or they evolved to use oxygen

Endosymbiotic Theory Belief is that eukaryotes formed approx. 2 billion years ago Prokaryotes “moved into” prokaryotic cells Created a symbiotic relationship One group was able to use oxygen to make ATP Mitochondria One group was able to use light to make sugars Chloroplasts

Evidence of the Endosymbiotic Theory Membranes of mitochondria and chloroplasts are similar to that of free-living prokaryotes Mitochondria and chloroplasts have DNA similar to bacterial DNA Ribosomes similar to those of bacteria Reproduce by binary fission

Sexual Reproduction The use of sexual reproduction by early organisms allowed evolution to occur at a much quicker rate More gene shuffling