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Eratosthenes used the sun’s rays which shone directly into a well but could not cast at all in Syene Egypt and he concluded that the sun was directly overhead. He also investigated the same idea in Alexandria, 7° 12′ from perpendicular to Syene- on the same meridian- and he found out that a shadow was cast in a well. He measured the distance between the two stadia and the height of the shadow at Alexandria and used the measurements to calculate the circumference of the earth. Ptolemy, on the other hand, revised the Eratosthenes’ calculation of earth’s circumference but estimated the earth’s circumference to be 28,985 kilometers (18,000 miles) which is an error of about 28% from that of Eratosthenes. Ptolemy’s circumference was therefore used throughout the Renaissance.
Eratosthenes circumference was more accurate than that of Ptolemy. Christopher Columbus used Ptolemy’s estimation to travel to the Far East by his voyage but he ended up in a continent hiding 28% error from his target. It means Eratosthenes calculations and estimation of the earth’s circumference was more accurate.
Finding the Northwest Passage by the Kingdoms of the Western Europe was essential because it provided a way establishing relationships with countries like China and America to trade with and make lots of wealth out of it. Christopher Columbus established such routes and founded the continent of America in 1492 through the coastal regions of Africa among other adventurers like Martin Frobisher and John Cabot.

Benjamin Franklin charted the Gulf map to help the continents explorers understand how to navigate the strong currents along the coasts of Mexico. He was addressing the question raised by the sailors to why some ship took too long to arrive at their destination than others. He was also addressing the importance of the strong currents that helped the ship kill the huge whales in the ocean. He located the strong currents and how to avoid it.
The Challenger expedition was used to describe the long voyage which took three and half years whereby the naval corvette covered a distance of 110840 kilometers. It was unique in that it carried out scientific investigation and discoveries of the oceans of the world. It originated all discoveries of the deep sea’s chemistry, oceanography, physics and biology.
Nansen was trying to solve the problem of ships submerging in the ocean. He became interested the scientific observations that had been made by the challenger expedition and he further wanted to ease the sled journey they had towards the North Pole. He wanted to describe the general characteristics of the polar region covered with ice that could trap the voyages.
Scientific methods such as carbon dating have been used to estimate the age of the earth. Biblical accounts have also played a significant role in gauging and estimating the age of the earth. The ever-changing estimates of the earth’s age are due to changes in some processes like sea levels, temperatures and salinity of the oceans hence making the information unreliable. The present estimates of the earth are likely to change due to various emerging and changing processes such as global warming and earthquakes that may change sea levels. The unreliable data that had been used in finding out the earth’s age and size may as well change over time.
The Earth is composed of 71% water, that is, seas, oceans, rivers, lakes and ponds among others on its surface. The land, on the other hand, contributes the remaining 29% which is the all-known land areas amongst which are continents and islands. The is high chance that water level may increase as the land mass decrease due to the global warming curve as the polar ice melt.
The Tropic of Cancer is the circle denoting the scope latitude 23.5 degrees north, where the sun is directly overhead at twelve on June 21, the start of summer in the northern side of the equator. The Tropic of Capricorn is the circle denoting the scope 23.5 degrees south where the sun is directly overhead at twelve on December 21, the start of winter in the northern side of the equator. At the point when the lines were named 2000 years back, the Sun was in the group of stars of Capricorn amid the winter solstice and Cancer amid the mid-year solstice (consequently the names). Presently because of the precession of the equinoxes the Sun is no longer in these heavenly bodies amid these circumstances. However, the names remain.
The Earth is the only planet with breathable oxygen in the atmosphere which supports life. The oxygen is put up in the atmosphere by plants and trees. It is also on Earth only where the level of carbon dioxide is low to regulate the temperature. In other planets like Venus, the temperature is too high due to lots of carbon dioxide. The climate of the earth is suitable for life existence. Other important factors found on earth and no other planets include the sun, ozone layer, light and magnetic field.

Work cited
Roller, Duane W., and Georgia L. Irby. “Eratosthenes’ Geography: Fragments Collected and Translated with Commentary and Additional Material.” Aestimatio: Critical Reviews in the History of Science 8 (2015): 170-178.
Rogers, A. D. “Pelagic ecology of the South West Indian Ocean Ridge seamounts: Introduction and overview.” Deep Sea Research Part II: Topical Studies in Oceanography 136 (2017): 1-4.