Earth’s Early History and Evolution of Multicellular Life

What features can you see on Earth’s surface in the photograph and the drawing?

Formation of the Earth Evidence shows that the Earth is about 4.6 Billion years old Earth was not “born” in a single event, but over time (100 million years) Large amounts of heat melted the particles that made up the Early Earth

Formation of the Earth The elements rearranged themselves according to density QUESTION: Where did the most dense elements go? Least dense?

Density Demo Material Density Rubbing Alcohol .79 Lamp Oil .80 Baby Oil .83 Vegetable Oil .92 Ice Cube Water 1.00 Milk 1.03 Dawn Dish Soap 1.06 Light Corn Syrup 1.33 Maple Syrup 1.37 Honey 1.42

Formation of the Earth The most dense elements formed the planet’s core The least dense elements (gases) formed the first atmosphere Hydrogen Nitrogen (no oxygen…yet!)

Formation of the Earth Early Earth’s atmosphere consisted of hydrogen cyanide, carbon dioxide, carbon monoxyide, nitrogen, hydrogen sulfide, and water.

Formation of the Earth Geologists infer that about 4 billion years ago, Earth cooled enough to form rocks Oceans did not exist because it was still too hot! (evaporation)

Formation of the Earth About 3.8 billion years ago, the Earth’s surface cooled enough for water to remain liquid (condensation) Now oceans covered most of the Earth’s surface

First Organic Molecules In the 1950s, chemists Miller and Urey tried to simulate conditions on the early Earth in a lab

The First Organic Molecules Over a few days, several amino acids (building blocks for proteins) began to accumulate Miller and Urey’s experiment showed that mixtures of organic compounds necessary for life could have arisen from simpler compounds found on primitive Earth!

The Puzzle of Life’s Origin It took about 200-300 million years after the Earth cooled to find cells that looked similar to modern bacteria QUESTION: How might these cells have originated?

The Puzzle of Life’s Origin Formation of Microspheres Under certain conditions large organic molecules can form tiny bubbles called proteinoid microspheres

The Puzzle of Life’s Origins Evolution of RNA and DNA There is some evidence that RNA may have existed before DNA Small sequences of RNA could have formed and replicated on their own

The RNA World Theory The theory is catalytic RNA can self replicate without enzymes and code for proteins. Scientists hypothesize that one of these proteins allowed RNA to convert into DNA.

Free Oxygen Microscopic fossils, or microfossils, of single-celled prokaryotic organisms have been found on rocks more than 3.5 billion years old They must have evolved in the absence of oxygen because Earth’s first atmosphere contained very little O2

Free Oxygen Over time, photosynthetic bacteria became common Oxygen combined with iron in the oceans and turned the oceans brown! The iron oxide fell to the ocean floor, the oceans became blue-green

Free Oxygen Oxygen began to accumulate in the atmosphere Ozone formed- O3 Created first “pollution” crisis! The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration

Endosymbiotic Theory Origin of Eukaryotic cells (cells with nuclei) Eukaryotic cells arose from living communities formed by prokaryotic organisms Lynn Margulis Mitochondria and Chloroplasts have similar DNA to bacteria Both have ribosomes Reproduce by binary fission

Endosymbiotic Theory