Answer:
Explanation:pon studying the Gubbio samples, Luis Alvarez wanted to know how long the foram extinction lasted before the species began to re-establish itself. He suggested the samples be handed over for analysis to another pair of Berkeley Lab scientists, nuclear chemists Frank Asaro and Helen Michel, who had developed a technique, called neutron activation analysis, that enabled precise measurements of very low concentrations of elements. Luis believed that neutron activation analysis would help determine how long it took for the clay layer to form. To the surprise of everyone involved, the measurements by Asaro and Michel showed that the clay layer was about 600 times richer in iridium than the surrounding limestone. Iridium, a silvery-white metal related to platinum, is virtually absent from the Earth’s crust, but high concentrations are common in extraterrestrial objects, such as asteroids.
The plot thickened when this same “iridium anomaly” was subsequently discovered in clay layers at locations in Denmark and New Zealand, and later dozens of other sites around the world where the geological record of the Cretaceous-Tertiary boundaries are also complete. These iridium-spiked layers of clay also contained an abundance of soot. Comparisons of ratios between iridium and several other key elements in the clay layers indicated that the widely scattered iridium anomalies all came from the same source – one that was not of this earth.
Brown v. Board of Education of Topeka was a landmark 1954 Supreme Court case in which the justices ruled unanimously that racial segregation of children in public schools was unconstitutional.
Answer:
mexican rebellion
Explanation:
they were claiming land we wanted and they rebeled
Answer:
Nast's drawings were instrumental in the downfall of Boss Tweed, the powerful Tammany Hall leader. As commissioner of public works for New York City, Tweed led a ring that by 1870 had gained total control of the city's government, and controlled "a working majority in the State Legislature".
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