Ectasian

{{short description|Second period of the Mesoproterozoic Era}}

{{Infobox geologic timespan

| name = Ectasian

| color = Ectasian

| top_bar = all time

| time_start = 1400

| time_end = 1200

| image_map = 1260 Ma paleoglobe.png

| caption_map = Map of Earth in the late Ectasian, c. 1260 Ma{{citation needed|reason=Description on Wikimedia Commons page is "own work" with no cited sources|date=June 2024}}

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| timeline = Ectasian

| name_formality = Formal

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| celestial_body = earth

| usage = Global (ICS)

| timescales_used = ICS Time Scale

| chrono_unit = Period

| strat_unit = System

| proposed_by =

| timespan_formality = Formal

| lower_boundary_def = Defined chronometrically

| lower_gssa_accept_date = 1991{{cite journal |last=Plumb |first=K. A. |date=June 1, 1991 |title=New Precambrian time scale |journal=Episodes |doi=10.18814/epiiugs/1991/v14i2/005 |volume=14 |issue=2 |pages=139–140|doi-access=free }}

| upper_boundary_def = Defined chronometrically

| upper_gssa_accept_date = 1991

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The Ectasian Period (from {{langx|grc|ἔκτασις|éktasis}}, meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from {{Period start|Ectasian}} Mya to {{Period start|Stenian}} Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

Geologically the name refers to the continued expansion of platform covers during this period. In the early Ectasian period, a day was 17 hours and 32 minutes. At the end of the Ectasian, it was 18 hours and 28 minutes.

This period is interesting for the first evidence of sexual reproduction. The 1.2-billion-year-old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells.

Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity. In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.