Early Earth and Beginnings of Life I. Physical forces and Life II. Formation of the Earth The Eagle Nebulae: nebulae.html This is the Eagle Nebula taken by the Hubble telescope on the first of April 1995. It is located in the constellation Serpens, the Snake, 7,000 light years from earth. A light year is the distance that light traveling at 186,000 miles per second goes in one year. The gaseous towers you see are several light years tall. Inside them the gas is dense enough that it collapses under its own weight to form stars. The young stars you see forming will grow as they accumulate more and more gas from their surroundings. Supernovae: supernovae.html This is an X-ray image of Keplerʼs star, a supernova that exploded in 1604. Cygnus Loop: presentdaysky.html Here you can see the Loop supernova in the constellation Cygnus, about 2,500 light years away from us. It exploded 20,000 years ago and is still expanding from that explosion. Oxygen shows up as blue, sulfur as red, and hydrogen as green; these are all elements important for the development of life. Asteroids: asteroid.html This stony asteroid, named Ida, was photographed on 28 August 1993 by the spacecraft of the Galileo expedition. It has a small moon, named Dactyl just to its right, and enlarged as an inset in the upper right hand part of the picture. Ida is about 50 miles in diameter and Dactyl less than one mile in diameter.
Note that even such a small asteroid as Ida has craters on its surface, evidence of having collided with smaller bodies. Comet: comet.html
This photograph is of Comet West, taken by John Laborde on March 9, 1976. Note that there are two distinct tails, a thin blue one made up of gases, and a broad white one made up of microscopic dust particles. Collisions: collisions.html This diagram shows a planetesimal on a collision course with the earth. When it strikes, the force of impact will cause the ocean to boil and produce an atmosphere of steam. Melting: melted.html This diagram shows a planetesimal striking the earth. Such impacts raised the temperature of surface rocks,melting the basalt and ejecting it into the sea and atmosphere where it reacted chemically with the water and atmospheric gases. Boiling: boiling.html The elevated temperature caused by the impact boiled the ocean, even at depths where the increased pressure raises the boiling point as high as 350 C. The only life that might have survived would have been subterranean thermophilic bacteria distant from the point of impact. Hydrogen Escape: escape.html The early atmosphere of the earth was dominated by carbon dioxide. Hydrogen was produced by chemical interaction between molten rock and atmospheric gases, but being very light escaped from the atmosphere into space. Volcanic Action: volcanic.html There was a high level of volcanic activity in the early days of the earth. Then, as now,
eruptions released a variety of gases containing compounds of carbon, sulfur and nitrogen into the atmosphere.
Moon Formation: moon.html A large planetesimal struck the earth and both bodies melted under the impact. Some of the molten material splashed up and began to orbit the earth. It accreted into one mass and formed the present moon. Any life that might have begun to develop would have been exterminated throughout the world. Craters: crater.html The moon was formed about 4.5 billion years ago, at a time when there was an abundance of planetesimals in the solar system. The pock-marked surface of the moon record its history of collisions with such objects. This is an oblique view of the far side of the moon photographed from the Apollo 11 spacecraft on July 16,1969. The large crater in the center is International Astronomical Union crater no. 308. It is 50 miles in diameter. Accretion: accretion.html In one sense, the accretionary phase is still in progress in the planetary system. Meteors still collide with earth and are incorporated into its mass. Each day about 4 billion particles, mostly dust-sized, enter the atmosphere and add several tons of mass to our planet. They burn up before hitting the ground and as they do, they leave a bright streak in the sky, such as the one shown here. These are called shooting stars. Larger meteors actually reach the ground before burning up entirely and these are known as meteorites. Collisions with bodies large enough to have a major impact are, fortunately, now rare. The most recent collision that seriously disrupted life was about 65 million years ago and caused massive extinction around the globe,including that of the dinosaurs (see Weeks 9 and 13). III. The conditions under which life originated
IV. How did life originate? Experiments: experiments.html This diagram shows the experimental apparatus used by two biochemists, Stanley Miller and Harold Urey, in the 1950s. They enclosed materials they believed to be components of the atmosphere of the early earth, such as water, methane, ammonia and hydrogen, in a closed chamber. Because high temperatures and frequent lightning were believed to have been characteristic of the early earth, they heated their mixture and subjected it to frequent electrical discharges. After a week they cooled the system
and condensed the products of the experiment. Amino acids and other organic molecules had been formed. Later experiments by other scientists using different mixtures that more closely reflected the improved knowledge of the components of early earth, have produced a wide variety of organic compounds, including all 20 amino acids, sugars, lipids, and nucleotide bases. These are the most important building blocks of life. Amino acids make up proteins, lipids form fats and oils, sugars are essential for metabolism, and the nucleotide bases are the building blocks of RNA and DNA, the material that organizes the construction and perpetuation of all living organisms. Hydrothermal vent: hydrothermal_vent.html Hydrothermal vents, also called geothermal vents, are submarine hot springs whose source of heat and minerals is the magma forming new oceanic crust. These hot springs spew plumes of hot water rich in chemicals that provide an alternative to the sun in supporting life in these dark abyssal depths (see Week 10). Depending on their chemical content, the plumes of vents can be black, like the one shown here, or white, grey or clear. The vent shown here is the first ever to be seen by humans. This photograph was taken in 1979 on the East Pacific Rise from the submersible Alvin. Microspheres: microspheres.html This photo, taken under the microscope shows tiny protobionts called microspheres that, although not living, do possess some of the properties of life. DNA: dna.html This model shows the structure of a DNA molecule. It is in a form called an alpha-helix, which is essentially two parallel strands, illustrated by the blue ribbons, connected to each other by various cross strands, and then the whole structure twisted like a spiral staircase. To reproduce itself, it unravels, and as it does, each strand takes from the environment the material necessary to construct the other half (illustrated by the orange ribbons),so that two identical alpha helices form in the place of one. V. The tree of life leading to animals