Earth temperature {temperature, Earth} increased until 130,000,000 years ago, then decreased until Ice Ages, and has remained almost the same since then. The year -8000 was warmest in recent history, until 20th century. Climate has been slowly cooling since then. Sea can rise or fall by 400 feet between Ice Age and warm period. Increased-volcanic-eruption periods correlate with Ice Ages, because volcanic dust reflects more sunlight and makes Earth cooler.
Strata can contain organic molecules {biomarker} from organism classes, because some cell-membrane lipids do not decompose.
Carbon isotopes are carbon-12, carbon-13, and carbon-14. Photosynthetic plants use more carbon-12 than carbon-13, so abundant plants lower carbon-12 ratio {isotope ratio, carbon} {carbon isotope ratio} in air. Air trapped in ancient rocks and ice can show relative amounts of photosynthetic plant life at past times.
Large meteors or comets and high volcanism can cause widespread death {catastrophe, Earth}.
meteor
Large meteor or comet hit 65 million years ago. Iridium level is higher in that rock stratum than in other layers. Iridium is more abundant in space than on Earth. That stratum also has pressure-shocked minerals.
volcanoes
Volcanic activity was high 443 million years ago, 374 million years ago, 251 million years ago, and 201 million years ago. Volcanoes put hydrogen sulfide, sulfur dioxide, carbon dioxide, and methane into air, which cause greenhouse effect and warm air.
ocean
With ocean warming, surface absorbs less oxygen, and chemocline rises. At high enough warming, chemocline comes to surface, and hydrogen sulfide enters air. Hydrogen sulfide kills land animals and plants directly. It also attacks ozone shield, allowing more UV radiation, which kills animals and plants.
Water absorbs oxygen. Water absorbs less oxygen at higher temperature, so oceans have less oxygen at surface and more at lower depths, which are cooler. At ocean bottoms, hydrogen sulfide comes from thermal vents. It rises and prevents further oxygen absorption at ocean depth {chemocline}. Below chemocline is high hydrogen sulfide, and above chemocline is high oxygen. Green sulfur bacteria and purple sulfur bacteria use hydrogen sulfide and are near ocean bottom. Photosynthetic organisms use dissolved carbon dioxide and sunlight so they stay near surface. Zooplankton use oxygen and so stay above chemocline.
Glaciers are largest every 100,000 years {glaciation era}, when Earth-axis tilt toward Sun minimizes, and perihelion shortest distance from Earth to Sun is in December in Northern Hemisphere, which has more land. Glaciers are smallest every 100,000 years, when Earth-axis tilt toward Sun maximizes, and perihelion shortest distance from Earth to Sun is in June in Northern Hemisphere, which has more land.
Continental {land mass} drift affects Earth temperature. When more land is in tropics, Earth absorbs more heat. When less land is at poles, glaciers decrease, reflective ice is less, and Earth reflects less heat.
Earth-axis tilt, axis wobble, and orbit cycles change sunlight amount that falls on Earth, in an overall cycle that caused Ice Ages {Milankovich model}. Earth-axis tilt cycles over 90,000 to 100,000 years. Earth axis wobble has a 39000-year to 42000-year cycle. Earth orbital path has a 17000-year to 21000-year cycle. Summer in Northern Hemisphere can be when Earth is closest to Sun, making hotter land temperatures.
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Date Modified: 2022.0225