Intense heat from the early core drove rapid and vigorous mantle convection so that crust quickly recycled into the mantle. The recycling of basaltic crust was so effective that no remnants of it are found today. One of the most unique features of planet Earth is its large Moon.
Unlike the only other natural satellites orbiting an inner planet, those of Mars, the Moon is not a captured asteroid. Astronomers have carried out computer simulations that are consistent with these facts and have detailed a birth story for the Moon. A little more than 4.
Earth was struck by a Mars-sized asteroid Figure below. The tremendous energy from the impact melted both bodies. The molten material mixed up.
The dense metals remained on Earth but some of the molten, rocky material was flung into an orbit around Earth. It eventually accreted into a single body, the Moon. Since both planetary bodies were molten, material could differentiate out of the magma ocean into core, mantle, and crust as they cooled. The Genesis Rock, with a date of 4.
At first, Earth did not have an atmosphere or free water since the planet was too hot for gases and water to collect. The atmosphere and oceans that we see today evolved over time. Most of these gases were drawn into the center of the solar nebula to form the Sun.
When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions.
Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system Figure below. It is called radiation because the genetically divergent descendants appear to radiate from a central point, much like the solar rays from the sun. During div-ergent evolution, descendants adopt a variety of characteristics that allow them to occupy similarly diverse niches.
The classic example of adaptive radiation is the study completed by Darwin as he observed 13 different finch species during his famous voyage of discovery to the Galapagos Islands. The islands themselves are well suited for adaptive radiation because they consist of numerous small islands in close proximity in the Pacific Ocean approximately miles kilometers west of Ecuador, South America.
Since Darwin's time, an analysis of the finch speciation revealed a founder population arrived from the mainland and occupied an island.
Specific island pressures probably caused that species to evolve into a new species different from the mainland species. As the finches overtook the island, competition increased, and pioneer species may have migrated to a different island. This created a new founder species that adapted to the new island pressures and modified to become a new species. Likewise, the remaining islands were colonized in succession. Because each island is slightly different, the finch adaptations were often unique to a specific island.
In addition, finches could return to an inhabited island and compete with the existing species, or return and divide territory, shelter, and resources and peacefully coexist.
The return to an inhabited island also probably sparked additional natural-selection pressures. We are still not sure how life originated on Earth. It could be a heavenly masterpiece, an astronomical anomaly, or a series of mutations and adaptations. There is evidence that favors each theory. Regardless, patterns in similarity appear to link some organisms more closely than others. Moulton, Ed. All rights reserved including the right of reproduction in whole or in part in any form. To order this book direct from the publisher, visit the Penguin USA website or call You can also purchase this book at Amazon.
Bionote Iron-containing rocks reportedly recovered from period strata contain no rust, further indicating the absence of oxygen. Bioterms Adaptive radiation is the process by which genetic diversity is increased in descendants of a common ancestor as they colonize and adapt to new territories.
See also:. Origin of Prokaryotes and Eukaryotes: Origin of Prokaryotes. Trending Here are the facts and trivia that people are buzzing about. Is Vatican City a Country? The Languages of Africa. These varied seafloor creatures - with bodies shaped like fronds, ribbons, and even quilts - lived alongside sponges for 80 million years.
Their fossil evidence can be found in sedimentary rocks around the world. However, the body plans of most Ediacaran animals did not look like modern groups. Douglas Erwin , using comparative developmental evidence, has examined whether any of the fossilized Ediacaran animals were related to modern animals. By the end of the Ediacaran, oxygen levels rose, approaching levels sufficient to sustain oxygen-based life. The early sponges may actually have helped boost oxygen by eating bacteria, removing them from the decomposition process.
Tracks of an organism named Dickinsonia costata suggest that it may have been moved along the sea bottom, presumably feasting on mats of microbes. However, about million years ago, most of the Ediacaran creatures disappeared, signaling a major environmental change that Douglas Erwin and other scientists are still working to understand. Evolving animal body plans, feeding relationships, and environmental engineering may have played a role.
Burrows found in the fossil record, dating to the end of the Ediacaran, reveal that worm-like animals had begun to excavate the ocean bottom. These early environmental engineers disturbed and maybe aerated the sediment, disrupting conditions for other Ediacaran animals. As environmental conditions deteriorated for some animals, they improved for others, potentially catalyzing a change-over in species.
The Cambrian Period million years ago witnessed a wild explosion of new life forms. Along with new burrowing lifestyles came hard body parts like shells and spines.
Hard body parts allowed animals to more drastically engineer their environments, such as digging burrows. A shift also occurred towards more active animals, with defined heads and tails for directional movement to chase prey. Active feeding by well-armored animals like trilobites may have further disrupted the sea floor that the soft Ediacaran creatures had lived on.
Unique feeding styles partitioned the environment, making room for more diversification of life. While Waptia scoured the ocean bottom, priapulid worms burrowed into the sediment, Wiwaxia attached to sponges, and Anomalocaris cruised above. Many of these odd-looking organisms were evolutionary experiments, such as the 5-eyed Opabinia. However, some groups, such as the trilobites, thrived and dominated Earth for hundreds of millions of years but eventually went extinct.
Stromatolite reef-building bacteria also declined, and reefs made by organisms called brachiopods arose as conditions on Earth continued to change.
However, despite all the changes that were to come, by the end of the Cambrian nearly all existing animal types, or phyla, mollusks, arthropods, annelids, etc. Skip to main content. Smithsonian Institution. Early Life on Earth — Animal Origins. An Oxygen Atmosphere When cyanobacteria evolved at least 2.
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