Mid Cretaceous period, when the Earth was flooded скачать в хорошем качестве

Mid Cretaceous period, when the Earth was flooded

*Earth’s highest sea levels occurred during the mid‑Cretaceous, when global oceans rose an estimated 200–300 meters above modern levels, flooding continents and creating vast shallow seas.* This extreme highstand reshaped land, climate, and ecosystems on a planetary scale, producing a warm, greenhouse world with no polar ice and dramatically altered habitats. --- 🌍 The Mid‑Cretaceous: Earth at Maximum Sea Level (~100 million years ago) 🌊 Why Sea Levels Became the Highest in Earth’s History *No polar ice sheets* — global temperatures were much warmer, so no major ice existed to store water. *Thermal expansion of seawater* — warm oceans physically expanded. *High seafloor spreading rates* — young, hot ocean crust displaced water upward. *Shallow ocean basins* — tectonics reduced basin capacity. *Sediment accumulation* — further reduced ocean volume. Together, these factors produced the **Cretaceous Highstand**, the highest sea level ever recorded. --- 🏞️ Land Effects: A Flooded World *Continents partially submerged* — up to one‑third of modern land was underwater. *Epicontinental seas* — shallow seas spread across continents, including the Western Interior Seaway covering central North America. *Reduced mountain ice and erosion* — warm climate meant lush lowlands and fewer glaciers. *Coastal ecosystems pushed inland* — beaches, mangroves, and deltas migrated hundreds of miles. Estimated global ratio: *Water:* ~70–75% *Land:* ~25–30% (Compared to today’s ~71% water / 29% land.) --- 🌿 How Plants and Animals Adapted *Tropical forests expanded poleward* — warm, humid conditions allowed palms and conifers to grow near the poles. *Marine reptiles diversified* — mosasaurs, plesiosaurs, and giant turtles dominated the seas. *Dinosaurs thrived on shrinking landmasses* — hadrosaurs, ceratopsians, and titanosaurs adapted to coastal plains and island-like habitats. *Plankton blooms increased* — warm seas boosted coccolithophores and ammonites. Adaptation estimates (conceptual, not numerically preserved in fossils): *Successful adaptation:* ~60–70% of species persisted through the Cretaceous. *Failed species:* ~30–40% turnover across the period (not a mass extinction, but high evolutionary churn). --- 🐋 Sea Life & Creature Size Warm, nutrient-rich shallow seas supported *giant marine reptiles* and large fish. Largest Sea Creatures of the Mid‑Cretaceous | Creature | Size | Notes | |---------|------|-------| | *Mosasaurus* | 50–56 ft | Apex marine reptile | *Elasmosaurus* | 45 ft | Extremely long-necked plesiosaur | *Kronosaurus* | 30–35 ft | Short‑necked, powerful predator | *Xiphactinus* | 15–20 ft | Giant predatory fish Sea creatures were *~20–40% larger on average* than similar ecological roles today due to warm waters and abundant prey. --- 🌧️ Rainfall & Climate The Cretaceous greenhouse climate produced: *High global humidity* *Intense monsoons* *Frequent tropical storms* Rainfall estimates (relative to modern averages): *Global precipitation:* ~10–20% higher *Tropics:* up to ~30% higher *Polar regions:* dramatically wetter (no ice caps) These are modeled estimates; direct percentages cannot be fossil‑verified. --- 🧬 Did Homo sapiens exist then? *No — humans did not exist.* Homo sapiens appeared only **~300,000 years ago**, long after the Cretaceous ended 66 million years ago. During the Cretaceous: No primates existed yet. Early mammals were small, nocturnal, and rodent‑like. --- 🐾 What Lived on Earth at This Time? Land Animals *Tyrannosaurs* *Hadrosaurs* *Ceratopsians* *Titanosaurs* *Small mammals* (shrew‑like) Plants *Conifers* *Ferns* *Flowering plants* (rapidly diversifying) *Mangroves and swamp forests* Sea Life *Ammonites* *Belemnites* *Plankton blooms* *Marine reptiles* (mosasaurs, plesiosaurs) --- 📉 Species Turnover & Evolutionary Change While not a mass extinction, the Cretaceous saw: *High evolutionary turnover* due to shifting coastlines and new habitats. *~30–40% species replacement* over tens of millions of years. *Rapid plant evolution* — flowering plants spread globally. *Marine ecosystem restructuring* — ammonites and marine reptiles diversified. --- Want to explore this era more deeply? Would you like to explore **a realistic reconstruction of Cretaceous Maryland**, **a breakdown of specific dinosaur ecosystems**, or **a comparison between Cretaceous and modern climate systems**?