Click me!! Origins of life

What happened first All this dust – 4.6 Billion Years Ago The earth is about 4.6 billion years old. This cartoon represents the origins of the universe. The early earth was a land of molten rock and violent volcanic activity. The earth’s crust was solidifying at this time, called the Hadean eon, since no rocks have been found that exceed 4.3 billion years old.

4.2 Billion years ago Lots o’ rain! 40 million years worth As the earth was forming, gasses were released from the molten core in volcanic activity. These gasses formed a cloud around the earth and were held as an atmosphere by the earth’s gravity. As the earth cooled and the crust formed the vapor condensed to liquid water and the rain began to fall. It rained such an enormous quantity over millions of years that the oceans of the world were formed. At first the earth was so hot that water was present only as a vapor.

4 billion years ago Primordial Soup . 4 billion years ago Primordial Soup The atmospheric gasses that were dissolved in the rain may have reacted with one another in the presence of the enormous amount of energy present on the planet to produce small organic molecules. There was no free oxygen, and no bacteria With the accumulation of the small organic compounds, the oceans became a thick, warm organic soup containing a variety of organic molecules Neither oxidation (there was no free oxygen) nor decay (there were no bacteria) would have destroyed these molecules and they would have accumulated in the oceans for hundreds of millions of years. With the accumulation of the small organic compounds, the oceans became a thick, warm organic soup containing a variety of organic molecules. The newly-formed organic molecules likely polymerized to produce still larger molecules and eventually a protocell arose. This structure would likely have had a lipid - protein membrane that carried on anaerobic energy metabolism and was a heterotroph (an organism that took in preformed food), fermenting the food with some degree of enzymatic activity. Once these protocells were self-replicating, they became true cells and biological evolution began.

2.5 billion years ago The evolution of photosynthesizing organisms caused oxygen to enter the atmosphere. Oxygen in the upper atmosphere formed ozone, which filtered UV light. The presence of oxygen also meant that most environments were unsuitable for anaerobic prokaryotes. Photosynthetic cyanobacteria and aerobic bacteria multiplied as new metabolic pathways evolved.

1.5-2 billion years ago Endosymbiont Recruitment Most likely the eukaryotic cell evolved from the prokaryotic cell, acquiring its organelles gradually. The nucleus may have developed by an invagination of the plasma membrane. Life was still aquatic at this point. The mitochondria may have been free-living aerobic prokaryotes and the chloroplasts may have been free-living cyanobacteria.

1 billion years ago Love at First Sight It is not known when multicellularity began but the first multicelled creatures were likely microscopic. Sexual reproduction would have its origins here and would have been an important first step toward the development of complex macroscopic organisms. The geologic period is the Precambrian era.

438 million years ago The Cambrian and Ordovician periods saw the marine algae and marine invertebrates flourish. During the Silurian period low lying primitive vascular plants appeared on land and the first jawed fishes appeared in the oceans. (408 to 438 million years ago) During the Devonian period, the first seed ferns appeared (360 - 408 million years ago).

248 million years ago MAMMALS!! The first reptiles appear in the Carboniferous period 286 - 360 million years ago During the Triassic period, the first dinosaurs and mammals appear (200 mya). Placental mammals appear during the Cretaceous period about 100 mya.

explains why some coastlines are mirror images of each other 175-225 million years ago The Continental Drift Theory continents are not fixed and instead, their positions have changed over time and continue to change. About 225 mya, the continents were joined to form one supercontinent called Pangea which then divided into two subcontinents. Land masses drift due to movement of slablike plates of the earth’s crust that float on a hot mantle layer. These slabs are called plates and their movement is called plate tectonics. The plates move because of seafloor spreading at ocean ridges. Continental drift explains why some coastlines are mirror images of each other

2 million years ago Monkey-like primates appear about 30 mya. The first hominids appear 2 – 6 mya Humans appear during the Pleistocene era, 2 mya.