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The evolution of Earth's radiogenic heat flow over time. The radioactive decay of elements in the Earth's mantle and crust results in production of daughter isotopes and release of geoneutrinos and heat energy, or radiogenic heat. About 50% of the Earth's internal heat originates from radioactive decay. [17]
The Martian atmosphere is composed mainly of carbon dioxide and has a mean surface pressure of about 600 pascals (Pa), much lower than the Earth's 101,000 Pa. One effect of this is that Mars' atmosphere can react much more quickly to a given energy input than Earth's atmosphere. [51]
Mars has only about 0.7% of the atmospheric pressure of Earth. Mars' atmosphere is about 6.5 millibar, Earth's atmosphere is 1013 millibar. Surface of Mars is like Earth at 100,000 feet (30 kilometres) in the stratosphere. [19] [20] Mars' atmosphere's humidity is 0.03%, Earth's average humidity is about 50% (lowest 0.36%, high 100%).
NASA scientists estimated that in 2024, Earth was about 2.65 degrees Fahrenheit (1.47 degrees Celsius) hotter than the average from the mid-19th century — a period from 1850 to 1900.
The effective radiation emission temperature is a related concept, [2] but focuses on the actual power radiated rather than on the power being received, and so may have a different value if the planet has an internal energy source or when the planet is not in radiative equilibrium. [3] [4]
An examination of the average global temperature changes by decades reveals continuing climate change: each of the last four decades has been successively warmer at the Earth's surface than any preceding decade since 1850. The most recent decade (2011-2020) was warmer than any multi-centennial period in the past 11,700 years. [16]: 2–6
This results in one hemisphere, the Southern, receiving more sunlight in summer and less in winter, and thus more extreme temperatures, than the Northern. When combined with Mars' much higher eccentricity compared to Earth, and far thinner atmosphere in general, Southern winters and summers are wider ranging than on Earth.
The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. [185] A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. [2] The gravitational potential difference and thus the delta-v needed to transfer between Mars and Earth is the second lowest for Earth ...