which is the first animal on the earth
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Answer:
In the Beginning
Today we take for granted that we live among diverse communities of animals that feed on each other. Our ecosystems are structured by feeding relationships like killer whales eating seals, which eat squid, which feed on krill. These and other animals require oxygen to extract energy from their food. But that’s not how life on Earth used to be.
With an environment devoid of oxygen and high in methane, for much of its history Earth would not have been a welcoming place for animals. The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things.
Evidence of microbes was also preserved in the hard structures (“stromatolites”) they made, which date to 3.5 billion years ago. Stromatolites are created as sticky mats of microbes trap and bind sediments into layers. Minerals precipitate inside the layers, creating durable structures even as the microbes die off. Scientists such as Smithsonian’s Dr Ian MacIntyre study today’s, rare living stromatolite reefs to better understand Earth’s earliest life forms.
Life Science Resources Early Life on Earth – Animal Origins
Illustration of animals near the ocean floor 510 million years ago. A large squid-like creature hovers over smaller organisms.
Depiction of one of Earth’s ocean communities, including the top predator Anomalocaris, during the Cambrian Period 510 million years ago. By the end of the Cambrian, nearly all the major groups of animals we know today (the phyla) had evolved. Depiction by Karen Carr, Smithsonian.
In the Beginning
Today we take for granted that we live among diverse communities of animals that feed on each other. Our ecosystems are structured by feeding relationships like killer whales eating seals, which eat squid, which feed on krill. These and other animals require oxygen to extract energy from their food. But that’s not how life on Earth used to be.
With an environment devoid of oxygen and high in methane, for much of its history Earth would not have been a welcoming place for animals. The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things.
Evidence of microbes was also preserved in the hard structures (“stromatolites”) they made, which date to 3.5 billion years ago. Stromatolites are created as sticky mats of microbes trap and bind sediments into layers. Minerals precipitate inside the layers, creating durable structures even as the microbes die off. Scientists such as Smithsonian’s Dr Ian MacIntyre study today’s, rare living stromatolite reefs to better understand Earth’s earliest life forms.
The First Animals
These clusters of specialized, cooperating cells eventually became the first animals, which DNA evidence suggests evolved around 800 million years ago. Sponges were among the earliest animals. While chemical compounds from sponges are preserved in rocks as old as 700 million years, molecular evidence points to sponges developing even earlier.
Oxygen levels in the ocean were still low compared to today, but sponges are able to tolerate conditions of low oxygen. Although like other animals, they require oxygen to metabolize, they don’t need much because they are not very active. They feed while sitting still by extracting food particles from water that is pumped through their bodies by specialized cells.
The simple body plan of a sponge consists of layers of cells around water-filled cavities, supported by hard skeletal parts. The evolution of ever more complex and diverse body plans would eventually lead to distinct groups of animals.
The assembly instructions for an animal’s body plan are in its genes. Some genes act like orchestra conductors, controlling the expression of many other genes at specific places and times to correctly assemble the components. While they were not played out immediately, there is evidence that parts of instructions for complex bodies were present even in the earliest animals.
Thanks to their hard skeletons, sponges became the first reef builders on Earth. Scientists like Smithsonian’s Dr Klaus Rüetzler are working to understand the evolution of the thousands of sponge species living on Earth today. PLEASE MARK AS BRAINLIEST.