The Early Cretaceous (

geochronological Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is pr ...

name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.

Geology

Proposals for the exact age of the Barremian-Aptian boundary ranged from 126 to 117 Ma until recently (as of 2019), but based on drillholes in

Svalbard Svalbard ( , ), also known as Spitsbergen, or Spitzbergen, is a Norwegian archipelago in the Arctic Ocean. North of mainland Europe, it is about midway between the northern coast of Norway and the North Pole. The islands of the group range ...

the defining early Aptian Oceanic Anoxic Event 1a (OAE1a) was carbon isotope dated to 123.1±0.3 Ma, limiting the possible range for the boundary to c. 122–121 Ma. There is a possible link between this anoxic event and a series of Early Cretaceous large igneous provinces (LIP). The Ontong Java- Manihiki- Hikurangi large igneous province, emplaced in the South Pacific at c. 120 Ma, is by far the largest LIP in Earth's history. The Ontong Java Plateau today covers an area of 1,860,000 km². In the Indian Ocean another LIP began to form at c. 120 Ma, the Kerguelen Plateau– Broken Ridge, together covering 2,300,000 km². Another LIP on the Liaodong Peninsula, China, 131–117 Ma, lasted for 10 million years. It was the result of the subduction of the

Kula Kula, which translates as ''Tower'' from Serbo-Croatian, may refer to: People *Bob Kula, American football player *Irwin Kula (born 1957), American rabbi and author *Karel Kula (born 1963), Czech footballer Places * Kula, Bihać, a village in ...

and Pacific plates, which was probably caused by a superplume. During the opening of the South Atlantic the Paraná–Etendeka LIP produced 1.5 million km³ of basalts and

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

s per year, beginning 133 Ma and lasting for a million years. The opening of the Central Atlantic continued as the Mid-Atlantic Ridge spread north to separate the Iberian Peninsula from the banks of

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

and to connect to the Canada Basin in the Arctic Ocean. With the opening of the Labrador Sea, Greenland became a separate tectonic plate and Laurentia became

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. The Proto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. The

Falkland Plateau Falkland may refer to: * Falkland, British Columbia, a community in Canada * Falkland, Nova Scotia, a community in Canada * Falkland Islands, an archipelago in the south Atlantic Ocean * Falkland, Fife, a former burgh in Fife, Scotland ** Falklan ...

broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In the

Panthalassic Ocean Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek "all" and "sea"), was the superocean that surrounded the supercontinent Pangaea, the latest in a series of supercontinents in the history of Earth. During the ...

the Pacific Plate continued to grow; the

Arctic Alaska-Chukotka terrane The Arctic Alaska-Chukotka terrane (AAC) is a microcontinent that today encompasses the North Slope, Brooks Range, and Seward Peninsula of northern Alaska; the Chukotka Peninsula, New Siberia Islands, and Wrangel Island in eastern Siberia; an ...

formed the Bering Strait. Continued rifting opened new basins in the Indian Ocean, separating India, Antarctica, and Australia. By 110 Ma the Mid-Atlantic Ridge reached south into the Proto-Caribbean and South Atlantic, effectively separating South America from Africa, and continued rifting in the northern end completed the longitudinal extent of the Atlantic. In Panthalassa the Ontong-Java Mega-LIP resulted in the formation of new tectonic plates and in the Indian Ocean the Kerguelen LIP began to push India northward.

Evolution

During this time many new types of dinosaur appeared or came into prominence, including

ceratopsia Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

ns, spinosaurids,

carcharodontosaurids Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

and coelurosaurs, while survivors from the Late Jurassic continued to persist.

Angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s (flowering plants) appeared for the first time during the Early Cretaceous; Archaefructaceae, one of the oldest fossil families (124.6 Ma) was found in the Yixian Formation, China. This time also saw the evolution of the first members of the Neornithes (modern birds). '' Sinodelphys'', a 125 Ma-old boreosphenidan mammal found in the Yixian Formation, China, is one of the oldest mammal fossils found. The fossil location indicates early mammals began to diversify from Asia during the Early Cretaceous. ''Sinodelphys'' was more closely related to metatherians (marsupials) than eutherians (placentals) and had feet adapted for climbing trees. '' Steropodon'' is the oldest

monotreme Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brain ...

(egg-lying mammal) discovered. It lived in

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

Geology

Evolution

See also

References

Notes

Sources