How far back does the fossil record extend?

Answer 1

Hard-bodied animals date back to the Cambrian era, about 540 million years ago.

However there are earlier advanced soft fossils found in recent years at places like Ediacara in Australia.

However, algae are known from about 3 billion years ago. These guys were the ones which invented photosynthesis, the important bit of which is splitting water into H and O. The O they discharge as waste, and the H they use to make complex biochemicals. When they evolved, the O2 component of the atmosphere was only a few%, and contained much CO2 and methane.

With their new trick of photosynthesis, the algae were able to mop up all (well, most of) the methane and CO2, and when these greenhouse gases disappeared, the world went into a Snowball Earth phase which lasted for a billion years or so, and the oceans were frozen at the Equator.

Much of the iron in the oceans which had been in solution, was precipitated out as iron oxide, and these form the banded iron deposits of great economic importance today.

But the volcanoes were still operating, and the methane and CO2 continued to increase, and eventually raised the temperature of the Earth.

The algae come in brown, red, and green varieties, and all our green plants may have descended from the green algae.

At the level of speculation, siderophile bacteria (which love iron) may have formed on the ocean bottom near Black Smokers, and these may evolve on iron-sulfur hydrothermal vents. These areas are rather inaccessible, and only in recent years have these speculations been offered.

Answer 2

The oldest known proto frog fossils are the fossils of Triadobatrachus massinoti. It existed 250 million years ago, about 30 million years before the first dinosaurs. T. massinoti lived in what is now Madagascar. It probably wasn't good at leaping.

The first true frog, Vieraella herbsti, was only 1.3 in long. It lived between 188 and 213 million years ago, at least 7 to 10 million years after the earliest known dinosaurs.

Answer 3

3.5 billion years old. They are microfossils that resemble certain bacteria that still exist today.

Answer 4

As far back as the Cryogenian era; about 850-635million years ago.

Answer 5

3.5 billion years