Answer:
C. Both observation 1 and observation 2.
Explanation:
The heliocentric model states that the Earth and planets revolve around the Sun at the center of the Solar System.
Observation 1 was answered by Nicolas Copernicus, father of the heliocentrism, in 1543. The reverse effect is an illusion created because the Earth revolves faster around the Sun than Mars.
And observation 2 also is explained by the model because the rotation of the earth made that the Stars be closer to it at different times of the year.
I hope this answer helps you.
The first step of the scientific method would be Observations.
Answer:
A. Along warm-water currents from warmer regions to colder regions
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Explanation:
Radioactive isotopes eventually decay, or disintegrate, to harmless materials. Some isotopes decay in hours or even minutes, but others decay very slowly. Strontium-90 and cesium-137 have half-lives of about 30 years (half the radioactivity will decay in 30 years). <u>Plutonium-239 has a half-life of 24,000 years.</u>
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<h3>What is radioactive decay? </h3>
Radioactive decay is the emission of energy in the form of ionizing radiation. The ionizing radiation that is emitted can include alpha particles, beta particles and/or gamma rays. Radioactive decay occurs in unbalanced atoms called radionuclides.
Elements in the periodic table can take on several forms. Some of these forms are stable; other forms are unstable. Typically, the most stable form of an element is the most common in nature. However, all elements have an unstable form. Unstable forms emit ionizing radiation and are radioactive. There are some elements with no stable form that are always radioactive, such as uranium. Elements that emit ionizing radiation are called radionuclides.
Learn more about Radioactive decay
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